Pre-paid cellular telephone system

Abstract
A pre-pay service unit uses pseudo-numbers to identify subscribers and
substitutes actual numbers to complete a call after verification of authenticity
and verification of a positive balance in a subscriber's account. The service
unit and the cellular telephone exchange data in the process of authentication.
For outgoing calls, a cellular telephone first transmits an "800" number and an
ANI. The "800" number is the telephone number of the pre-pay service unit, which
then requests number actually dialed. The cellular telephone responds with
dialed digits, a security code, and status data. If the information is correct,
the dialed digits are then passed to a local exchange carrier to complete the
call. For incoming calls, a pseudo-number directs the call to the pre-pay
service unit, which converts the pseudo-number to the actual telephone number of
a subscriber's cellular telephone.

      Inventors: Fougnies; Douglas V. (Tempe, AZ)
      Assignee: Cellexis International, Inc. (AZ)
      Appl. No.: 104420
      Filed: June 25, 1998

      Current U.S. Class:455/406; 379/114.2; 379/127.06; 455/408; 455/411
      Intern'l Class: H04M 011/00
      Field of Search: 455/406,408,407,409,410,418,419,564 ;127.03;127.06;144.01
      379/144,114,130,113,112,127,355,356,114.03,114.01,114.2,114.16,127.01,127.02

 

 

References Cited [Referenced By]

 

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Primary Examiner: Legree; Tracy
Attorney, Agent or Firm: Fish & Richardson P.C.

 

Parent Case Text

 

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 08/569,961,
filed Dec. 8, 1995, now U.S. Pat. No. 5,778,313.

Claims

 

What is claimed as the invention is:

1. A method, performed by a wireless communication device, of facilitating
pre-authorized wireless communications, the method comprising routing a call
request through a pre-authorized wireless service provider by transmitting a
predetermined destination number in place of a subscriber-specified destination
number, in which the transmission of the predetermined destination number is
transparent to the subscriber, and in which the pre-authorized wireless service
provider comprises a pre-pay service unit.

2. The method of claim 1 in which the predetermined destination number
corresponds to a pre-authorized wireless service provider.

3. The method of claim 2 in which the predetermined destination number comprises
a toll-free number.

4. The method of claim 1 in which the subscriber-specified destination number
corresponds to a party with whom communications are desired.

5. The method of claim 1 in which the routing further comprises:

buffering the subscriber-specified destination number; and

transmitting the buffered subscriber-specified number to the pre-authorized
wireless service provider.

6. The method of claim 5 in which transmitting the buffered subscriber-specified
number comprises:

receiving a request from the pre-authorized wireless service provider; and

sending the buffered subscriber-specified number in response to the received
request.

7. The method of claim 1 further comprising transmitting a wireless
communication device identifier with the predetermined destination number.

8. The method of claim 7 in which the wireless communication device identifier
and the predetermined destination number are transmitted serially.

9. The method of claim 7 in which the predetermined destination number
facilitates connection to the pre-authorized wireless service provider and the
wireless communication device identifier enables the pre-authorized wireless
service provider to determine the wireless communication device's identity.

10. The method of claim 1 in which the wireless communication device comprises a
cellular telephone.

11. A method, performed by a wireless communication device, of facilitating
pre-authorized wireless communications, the method comprising

routing a call request through a pre-authorized wireless service provider by
transmitting a predetermined destination number in place of a
subscriber-specified destination number, in which the pre-authorized wireless
service provider comprises a pre-pay service unit;

in which the routing further comprises buffering the subscriber-specified
destination number, and transmitting the buffered subscriber-specified number to
the pre-authorized wireless service provider; and

further comprising transmitting security information to the pre-authorized
wireless service provider.

12. The method of claim 11 in which the transmitted security information enables
the pre-authorized wireless service provider to verify the wireless
communication device's authenticity.

13. A method, performed by a wireless communication device, of facilitating
pre-authorized wireless communications, the method comprising

routing a call request through a pre-authorized wireless service provider by
transmitting a predetermined destination number in place of a
subscriber-specified destination number, in which the pre-authorized wireless
service provider comprises a pre-pay service unit;

in which the routing further comprises buffering the subscriber-specified
destination number, and transmitting the buffered subscriber-specified number to
the pre-authorized wireless service provider; and

further comprising transmitting roaming information to the pre-authorized
wireless service provider.

14. A method, performed by a wireless communication device, of facilitating
pre-authorized wireless communications, the method comprising routing a call
request through a pre-authorized wireless service provider by transmitting a
predetermined destination number in place of a subscriber-specified destination
number, and further comprising transmitting a wireless communication device
identifier with the predetermined destination number, in which the wireless
communication device identifier comprises an ANI, and in which the
pre-authorized wireless service provider comprises a pre-pay service unit.

15. A method, performed by a wireless communication device, of facilitating
pre-authorized wireless communications, the method comprising routing a call
request through a pre-authorized wireless service provider by transmitting a
predetermined destination number in place of a subscriber-specified destination
number, and further comprising transmitting a wireless communication device
identifier with the predetermined destination number, in which the wireless
communication device identifier comprises information other than an ANI, and in
which the pre-authorized wireless service provider comprises a pre-pay service
unit.

16. A method, performed by a wireless communication device, of facilitating
pre-authorized wireless communications, the method comprising routing a call
request through a pre-authorized wireless service provider by transmitting a
predetermined destination number in place of a subscriber-specified destination
number, in which the pre-authorized wireless service provider comprises a
pre-pay service unit.

17. Software, stored in a computer-readable medium, comprising instructions to
cause a wireless communications device to perform the following operations:

receive a subscriber-specified destination number;

buffer the received subscriber-specified destination number;

transmit a predetermined destination number in place of the buffered
subscriber-specified destination number; and

transmit the buffered subscriber-specified destination number to the
pre-authorized wireless service provider comprising a pre-pay service unit;

in which transmission of the predetermined destination number is transparent to
a subscriber operating the wireless communication device.

18. The software of claim 17 in which transmission of the predetermined
destination number occurs in response to a trigger event.

19. The software of claim 18 in which the trigger event comprises a depression
of a SEND key on a wireless communications device.

20. The software of claim 17 in which the received subscriber-specified
destination number corresponds to subscriber input on a keypad of the wireless
communications device.

21. The software of claim 17 in which the received subscriber-specified
destination number corresponds to a party to be contacted.

22. The software of claim 17 in which the predetermined destination number
corresponds to a pre-authorized wireless service provider.

23. The software of claim 17 further comprising instructions to perform the
following operations:

receive a request for the subscriber-specified destination number from the
pre-authorized wireless service provider; and

transmit the buffered subscriber-specified destination number to the
pre-authorized wireless service provider in response to the received request.

24. Software, stored in a computer-readable medium, comprising instructions to
cause a wireless communications device to perform the following operations:

receive a subscriber-specified destination number;

buffer the received subscriber-specified destination number; and

transmit a predetermined destination number in place of the buffered
subscriber-specified destination number;

further comprising instructions to perform the following operations:

receive a request for the subscriber-specified destination number from a
pre-authorized wireless service provider; and

transmit the buffered subscriber-specified destination number to the
pre-authorized wireless service provider comprising a pre-pay service unit in
response to the received request; and

further comprising instructions to transmit security information to the
pre-authorized wireless service provider in response to the received request,
the security information comprising data that enables the pre-authorized
wireless service provider to verify the authenticity of the wireless
communication device.

25. Software, stored in a computer-readable medium, comprising instructions to
cause a wireless communications device to perform the following operations:

receive a subscriber-specified destination number;

buffer the received subscriber-specified destination number; and

transmit a predetermined destination number in place of the buffered
subscriber-specified destination number;

further comprising instructions to perform the following operations:

receive a request for the subscriber-specified destination number from a
pre-authorized wireless service provider comprising a pre-pay service unit; and

transmit the buffered subscriber-specified destination number to the
pre-authorized wireless service provider in response to the received request;
and

further comprising instructions to transmit roaming information to the
pre-authorized wireless service provider in response to the received request.

26. Software, stored in a computer-readable medium, comprising instructions to
cause a wireless communications device to perform the following operations:

receive a subscriber-specified destination number;

buffer the received subscriber-specified destination number; and

transmit a predetermined destination number in place of the buffered
subscriber-specified destination number;

further comprising instructions to transfer a wireless communication device
identifier with the predetermined destination number, the wireless communication
device identifier comprising data that enables a pre-authorized wireless service
provider comprising a pre-pay service unit to identify the wireless
communication device.

27. The software of claim 26 in which the wireless communication device
identifier comprises an ANI.

28. A method, performed by a wireless communication device, of facilitating
pre-authorized wireless communications, the method comprising:

receiving from a subscriber a destination number specifying a party to be
called;

buffering the destination number received from the subscriber;

transmitting a predetermined pre-authorized wireless service provider's number
in place of the buffered destination number;

receiving a request for the subscriber-specified destination number from the
pre-authorized wireless service provider; and

transmitting the buffered destination number to the pre-authorized wireless
service provider in response to the received request;

in which transmission of the predetermined pre-authorized wireless service
provider's number is transparent to a subscriber operating the wireless
communication device,

and in which the pre-authorized wireless service provider comprises a pre-pay
service unit.

29. A method, performed by a wireless communication device, of facilitating
pre-authorized wireless communications, the method comprising:

transparently receiving from a pre-authorized wireless service provider security
information corresponding to an incoming call request;

verifying the received security information; and

selectively notifying a subscriber of an incoming call only after the security
information is verified.

30. The method of claim 29 in which the selective notification comprises
notifying the subscriber if the received security information is verified to be
valid.

31. The method of claim 29 further comprising, upon verification of the received
security information, transmitting verification information to the
pre-authorized wireless service provider.

32. The method of claim 29 in which the transparent reception of the security
information comprises going off-hook without alerting the subscriber.

33. Software, stored in a computer-readable medium, comprising instructions to
cause a wireless communications device to perform the following operations:

receive transparently from a pre-authorized wireless service provider security
information corresponding to an incoming call request;

verify the received security information; and

selectively notify a subscriber of an incoming call only after the security
information is verified.

34. The method of claim 33 in which the selective notification comprises
notifying the subscriber if the received security information is verified to be
valid.

35. The software of claim 33 further comprising instructions to transmit
verification information to the pre-authorized wireless service provider upon
verification of the received security information indicating acceptance.

36. The software of claim 33 in which the transparent reception of the security
information comprises executing instructions to go off-hook without alerting the
subscriber.

37. A method, performed at a pre-authorized wireless service provider, of
facilitating pre-authorized wireless communications, the method comprising:

receiving a call from a wireless communication device directed to a
predetermined destination number, the call including information that identifies
the wireless communication device;

accessing a pre-paid account corresponding to the wireless communication device;
and

transparently obtaining a subscriber-specified destination number from the
identified wireless communication device;

in which the transmission of the predetermined destination number is transparent
to a subscriber operating the wireless communication device.

38. The method of claim 37 in which the predetermined destination number
corresponds to the pre-authorized wireless service provider.

39. The method of claim 37 in which the subscriber-specified destination number
corresponds to a party with whom communications are desired.

40. The method of claim 37 further comprising confirming that the identified
wireless communication device corresponds to a subscriber of the pre-authorized
wireless service provider.

41. The method of claim 37 in which transparently obtaining the
subscriber-specified number comprises communicating with the wireless
communication device in a manner that is unnoticeable to a subscriber.

42. The method of claim 37 further comprising:

determining a status of an account corresponding to the identified wireless
communication device; and

based on a result of the determining, selectively passing the
subscriber-specified destination number to a public network.

43. The method of claim 37 further comprising passing the subscriber-specified
destination number to a public network.

44. A method, performed at a pre-authorized wireless service provider, of
facilitating pre-authorized wireless communications, the method comprising:

receiving a call from a wireless communication device directed to a
predetermined destination number, the call including information that identifies
the wireless communication device;

accessing a pre-paid account corresponding to the wireless communication device;
and

transparently obtaining a subscriber-specified destination number from the
identified wireless communication device;

in which the information that identifies the wireless communication device
comprises an ANI.

45. A method, performed at a pre-authorized wireless service provider, of
facilitating pre-authorized wireless communications, the method comprising:

receiving a call from a wireless communication device directed to a
predetermined destination number, the call including information that identifies
the wireless communication device;

accessing a pre-paid account corresponding to the wireless communication device;
and

transparently obtaining a subscriber-specified destination number from the
identified wireless communication device; and

further comprising receiving security information from the identified wireless
communication device.

46. The method of claim 45 further comprising verifying authenticity of the
wireless communication device based on the security information received.

47. The method of claim 46 further comprising selectively passing the
subscriber-specified destination number to a public network based on a result of
the authenticity verification.

48. The method of claim 47 in which the subscriber-specified destination number
is not passed to the public network if the authenticity of the wireless
communication device is not verified.

49. A method, performed at a pre-authorized wireless service provider, of
facilitating pre-authorized wireless communications, the method comprising:

receiving a call from a wireless communication device directed to a
predetermined destination number, the call including information that identifies
the wireless communication device;

accessing a pre-paid account corresponding to the wireless communication device;
and

transparently obtaining a subscriber-specified destination number from the
identified wireless communication device; and further comprising:

determining a status of an account corresponding to the identified wireless
communication device; and

based on a result of the determining, selectively passing the
subscriber-specified destination number to a public network

in which the subscriber-specified destination number is not passed to the public
network if the account contains insufficient funds.

50. The method of claim 49 further comprising receiving security information
from the identified wireless communication device.

51. The method of claim 50 further comprising verifying authenticity of the
wireless communication device based on the security information received.

52. The method of claim 51 further comprising selectively passing the
subscriber-specified destination number to a public network based on a result of
the authenticity verification.

53. The method of claim 52 in which the subscriber-specified destination number
is not passed to the public network if the authenticity of the wireless
communication device is not verified.

54. A method, performed at a pre-authorized wireless service provider, of
facilitating pre-authorized wireless communications, the method comprising:

receiving in connection with a call request a pseudo-number from a calling
party;

based on the received pseudo-number, determining a subscriber destination number
of a wireless communication device associated with the pre-authorized wireless
service provider;

passing the subscriber destination number to a public network to complete the
call request.

55. The method of claim 54 in which the public network comprises a local
exchange carrier (LEC) or a mobile telephone switching office (MTSO) or both.

56. The method of claim 54 in which the pseudo-number comprises a destination
number for the pre-authorized wireless service provider.

57. The method of claim 54 in which the pseudo-number uniquely identifies the
subscriber.

58. The method of claim 54 in which the subscriber destination number comprises
a Mobile Identification Number (MIN).

59. The method of claim 54 in which determining the subscriber destination
number comprises using the received pseudo-number as an index to a look-up
table.

60. The method of claim 54 further comprising, prior to passing the subscriber
destination number to the public network, confirming a status of an account
associated with the subscriber destination number.

61. The method of claim 60 in which confirming the account status comprises
determining if the account contains sufficient funds.

62. The method of claim 61 further comprising prohibiting completion of the call
request if the account contains insufficient funds.

63. The method of claim 54 further comprising transmitting a security code to
the wireless communication device via the public network.

64. The method of claim 63 further comprising receiving from the wireless
communication device a verification code corresponding to the transmitted
security code.

65. The method of claim 64 comprising confirming the verification code and
aborting the call request if the verification code does not confirm
successfully.

66. The method of claim 54 further comprising monitoring a status of an account
associated with the wireless subscriber device during the call.

67. The method of claim 54 in which the pseudo-number is distinct from the
subscriber destination number.

Description

 

BACKGROUND OF THE INVENTION

This application relates to U.S. application Ser. No. 08/559,283, filed Nov. 15,
1995, which is a continuation-in-part of U.S. application Ser. No. 08/364,479,
filed Dec. 23, 1994, now U.S. Pat. No. 5,722,067.

This invention relates to a cellular telephone system that allows only pre-paid
subscribers to complete cellular telephone calls and, in particular, to a fraud
resistant, pre-paid subscriber system that does not require special hardware
connections to existing telephone networks.

A cellular telephone is a multi-frequency, portable transceiver, typically
constructed with state of the art integrated circuits and capable of
transmitting voice and digital data reliably almost anywhere in the world.
Except for cost, a cellular telephone would likely be the appliance of choice
for every person in the country. A cellular telephone costs at least three times
as much, per month, as a "land line," i.e. as a telephone connected by wire to a
public switching network. Despite the sophistication and quality of cellular
telephones, the relatively high cost of a cellular telephone is not the
telephone itself but the charges for the use of the telephone. Unfortunately, a
significant portion of the cost of the system is due to theft of services and
many techniques for detecting or thwarting theft have been proposed or
implemented.

Some security systems rely on calling patterns to detect theft and such systems
are prone to false positives, i.e. incorrectly identifying a legitimate call as
an illegal call. Also, such systems require a number of calls to detect theft,
which means that, if the calls were illegal, the cost of the calls must be
absorbed by someone other than the caller. It is preferred to have a system that
can detect theft of service as soon as the theft is attempted.

Another aspect of cost is the ability of a subscriber to pay for services
compared to the subscriber's desire to use the services. Many subscribers sign
up on the basis that the cellular telephone will only be used for emergencies
and then find themselves defining "emergency" progressively more broadly. For
many subscribers, it has been found beneficial to provide a pre-paid
subscription that is self-limiting in the sense that the service is terminated
when the payments are used up. U.S. Pat. No. 5,353,335 (D'Urso et al.) describes
a modified network architecture in which a special platform for pre-paid calling
service is connected to a node in a public, switched telephone network.

The above-identified, related application also describes a pre-paid, cellular
system. The system disclosed in the application requires no modification to
cellular telephones and, for outgoing calls, uses the automatic number
identification (ANI) from each cellular telephone as a file link to identify and
to authenticate the cellular telephone. Incoming calls are transferred to the
mobile telephone switching office (MTSO) in which a number of lines are reserved
for pre-paid subscribers. An incoming call is screened for a valid number and a
positive, pre-paid balance by the subscription service and is then passed on to
the subscriber. If the MTSO will not dedicate lines to pre-paid subscribers, a
significant geographic area is unavailable to a specific but viable market.

A system requiring no modification to the cellular telephone is most easily
implemented but the security of such a system is not as great as when the
cellular telephone is modified. A problem with a system requiring modification
to the cellular telephone is that physical access to the telephone is required.

In view of the foregoing, it is therefore an object of the invention to provide
a cellular telephone system for pre-paid subscribers in which the system is
transparent to existing telephone networks.

Another object of the invention is to provide a pre-paid subscription service
that detects theft as it occurs and terminates the call.

A further object of the invention is to provide a pre-paid cellular telephone
system that monitors both outgoing and incoming calls without the need for
dedicated lines at an MTSO.

Another object of the invention is to provide a secure, pre-paid cellular
telephone system requiring only software modification to existing cellular
telephones to adapt the telephones to the system.

A further object of the invention is to provide a secure cellular telephone
system in which modifications to a cellular telephone do not require physical
access to the telephone.

SUMMARY OF THE INVENTION

The foregoing objects are achieved in this invention in which a pre-pay service
unit uses pseudo-numbers to identify subscribers and substitutes actual numbers
to complete a call after verification of authenticity and verification of a
positive balance in the subscriber's account. The service unit and the cellular
telephone exchange data in the process of authentication. The pseudo-numbers are
combined with other data to provide a secure check of the identity of the
cellular telephone and the authenticity of the call. It has been found that
modifying a cellular telephone to share identification between the system and
the telephone increases the security of the system and enables the operation of
the system to be transparent to an MTSO.

In particular, for outgoing calls, the cellular telephone first transmits an
"800" number and the ANI. The "800" number is the telephone number of a pre-pay
service unit which receives the call. A switching network in the service unit
then requests the dialed number, which the cellular telephone transmits with a
security code and status data. If the data is authentic, the dialed digits are
then passed to a local exchange carrier to complete the call. For incoming
calls, a pseudo-number directs the call to a pre-pay service unit, which
converts the pseudo-number to the actual telephone number of a subscriber's
cellular telephone. After exchanging data with the subscriber's telephone, and
after verifying authenticity and credit balance, the call is completed. Both
incoming and outgoing calls can be monitored for charges and a call is
terminated if a subscriber's balance reaches zero.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention can be obtained by considering
the following detailed description in conjunction with the accompanying
drawings, in which:

FIG. 1 illustrates an outgoing call from a cellular telephone in accordance with
the prior art;

FIG. 2 illustrates an outgoing call from a cellular telephone in accordance with
the invention;

FIG. 3 illustrates an incoming call to a cellular telephone in accordance with
the prior art;

FIG. 4 illustrates an incoming call to a cellular telephone in accordance with
the invention;

FIG. 5 is a flow chart of an outgoing call in accordance with a preferred
embodiment of the invention;

FIG. 6 is a flow chart of an incoming call in accordance with a preferred
embodiment of the invention;

FIG.7 is a block diagram of a cellular telephone suitable for use in the
invention; and

FIG. 8 is a block diagram of the apparatus used by the pre-pay service unit.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an outgoing call from a cellular telephone to a conventional
telephone. Cellular telephone 10 transmits the dialed number followed by the
automatic number identification code that uniquely identifies telephone 10. This
data is received by mobile telephone switching office 12, wherein the number is
verified as a valid subscriber and, if so, the call is transferred to local
exchange carrier 14. Local exchange carrier 14 switches the call to the
appropriate land line connecting carrier 14 with telephone 16.

FIG. 2 illustrates the path of an outgoing call from a pre-pay subscriber
through a pre-pay service unit. The subscriber enters the desired destination
telephone number on cellular telephone 20 and then presses the "send" button.
Telephone 20 displays the dialed number but actually transmits a pseudo-number,
viz. an "800" number to mobile telephone switching office 12, followed by the
automatic number identification code of cellular telephone 20. The pseudo-number
is the number of a pre-pay service unit. An "800" number is used to obtain the
automatic number identification code of telephone 20.

Switching office 12 passes the call through local exchange carrier 14 and tandem
switch 22 to pre-pay service unit 24. Service unit 24 recognizes the automatic
number identification as a pre-pay subscriber and transmits back to cellular
telephone 20 a request for the number actually dialed. Cellular telephone 20
responds with the dialed number, which passes through switching office 12,
carrier 14, switch 22, and service unit 24 to local exchange carrier 26, which
switches the call to the appropriate land for connection to telephone 16. Thus,
the number initially transmitted by a pre-paid subscriber is the number of a
pre-pay service unit, which then completes the call with the dialed number. In
the process, the pre-pay service unit monitors the calls and the account of the
subscriber to be sure that the call is genuine and that the account of the
subscriber has a positive balance.

In FIGS. 1-4, a pre-pay subscriber is indicated by a cellular telephone symbol
and a non pre-pay subscriber is represented by a symbol of a conventional
telephone. This is solely for the sake of clarity. A pre-pay subscriber can call
anyone, including another subscriber. An outgoing call from a subscriber's
telephone is always a call to an "800" number and, therefore, always includes
the dialed number and the automatic number identification code. This
characteristic of cellular telephone service is used to direct all outgoing
calls to the pre-pay service unit, enabling the pre-pay service unit to monitor
all subscriber calls for authenticity and appropriate charges.

FIG. 3 illustrates an incoming call to a cellular telephone in accordance with
the prior art. In this case, the user dials the destination number on telephone
16 and the number is recognized as a cellular telephone number by local exchange
carrier 14. Carrier 14 transfers the call to mobile telephone switching office
12, which then authenticates the call and pages cellular telephone 10.

In accordance with the invention, the actual telephone number of the cellular
phone is known only by the pre-pay service unit and a pseudo-number is provided
to the public, including the subscriber. The pseudo-number is actually a number
belonging to the pre-pay service unit. Thus, as illustrated in FIG. 4, a user
dials the pseudo-number on telephone 16 and local exchange carrier 26 recognizes
the number as belonging to pre-pay service unit 24. Upon receipt of the incoming
call, pre-pay service unit 24 looks up the actual number of cellular telephone
20 in a conversion table and transfers the number to local exchange carrier 14.
Carrier 14 recognizes the number as a cellular number and passes the call to
mobile telephone switching office 12 which authenticates the number and pages
cellular telephone 20.

For both incoming and outgoing calls, the pre-pay service unit is interposed in
the path of a call and converts the dialed number into a second number for
completing the telephone call. The pre-pay service unit is independent of the
mobile telephone switching office and is connected into the system by way of
land lines or its own cellular connections.

While intercepting telephone calls to or from a subscriber, the pre-pay service
unit exchanges data with the subscriber cellular telephone prior to completing
the call. The data exchange between the pre-pay service unit and a subscriber's
cellular telephone is illustrated in FIGS. 5 and 6. In FIGS. 5 and 6, a small
dot in the lower left hand corner of a rectangle indicates an action by the
subscriber's cellular telephone. A small dot in the lower right hand corner of a
rectangle indicates an action taken by the pre-pay service unit. A rectangle
with a dot in neither location represents an action taken by a public switching
network.

FIG. 5 is a flow chart of an outgoing call from a subscriber's cellular
telephone. In step 51, the subscriber dials the desired phone number. If the
cellular telephone has a display, the dialed number is displayed. In step 52,
the subscriber's cellular telephone actually transmits an "800" number followed
by the automatic number identification code. The telephone call is passed to the
pre-pay service unit, which stores the automatic number identification and opens
a channel to the subscriber's telephone. The pre-pay service unit then requests
the dialed number (step 54) and the subscriber's telephone responds (step 55)
with the number actually dialed and other data, such as roaming information, and
a security code. "Roaming" is the situation in which the cellular telephone is
outside of the service area of the subscriber. Service within the area is
considered a local call and service outside the area is subject to additional
charges for "roaming" and long distance.

After receiving the data from the subscriber's telephone, the pre-pay service
unit uses the automatic number identification to check the subscriber's account
for a positive balance and verifies the automatic number identification code
with the security code transmitted by the subscriber's telephone. If there is a
positive balance and the codes are authentic, the pre-pay service unit sends an
"off hook" signal to the mobile telephone switching office, step 57, and
transfers the call to the local exchange carrier, step 58, completing the call.

FIG. 6 illustrates the exchange of information between the pre-pay service unit
and a subscriber's cellular telephone for an incoming call. In step 61, a party
dials what he believes is the actual telephone number of a subscriber's cellular
telephone. In step 62, the local exchange carrier recognizes the number as
belonging to the pre-pay service unit and transfers the call accordingly. In
step 63, the pre-pay service unit looks up the pseudo-number in a table and
replaces the pseudo-number with the actual number of the subscriber's telephone.
In step 64, the pre-pay service unit checks the subscriber's account for a
positive balance, based upon the actual number of the subscriber, also known as
the mobile identification number (MIN).

In step 65, the pre-pay service unit retrieves a security code for the
subscriber's account and then passes the actual telephone number to a local
exchange carrier (step 66). The carrier passes the call to a mobile telephone
switching office for paging the subscriber's cellular telephone. upon receipt of
the page, the subscriber's telephone goes off-hook, in what is known as
auto-answer mode, but does not ring. In other words, the subscriber's cellular
telephone must have the features of auto answer and silent ring. These features
are used in many, but not all, commercially available cellular telephones. To be
compatible with the invention, a cellular telephone must have both features.

After the subscriber's telephone goes off-hook, the pre-pay service unit sends a
security code to the subscriber's telephone, step 73. The subscriber's telephone
verifies the code, step 74, sends a verification code to the pre-pay service
unit and provides an audible ring, step 75. The pre-pay service unit verifies
the code and monitors the account of the subscriber for call duration and
billing. The subscriber "answers" the telephone call by pressing "send", step
77.

The exchange of data between the subscriber's telephone and the pre-pay service
unit makes it very difficult to steal services. If desired, the data transferred
between the subscriber's telephone and the prepay service unit can be scrambled
or encrypted. For example, in step 55 (FIG. 5) the DID number, roam code, and
security code need not be sent consecutively but can be mixed in a predetermined
sequence and sent as a single block of data. Similarly, the subscriber's
telephone can verify the code (step 74, FIG. 6) as it is received from the
pre-pay service unit or it can re-order the digits in a predetermined manner
prior to verification. Alternatively, one can use a checksum to verify the
digits or a checksum of selected digits for verification. The particular manner
for scrambling or encrypting data is a matter of choice.

FIG. 7 illustrates a cellular telephone suitable for use in the invention. In
particular, cellular telephone 80 includes microprocessor 81 coupled to memory
82 and to an I/O device such as encoder 83 and transceiver 84. Antenna 85 is
coupled to transceiver 84 for emitting the high frequency radio waves that
couple cellular telephone to the mobile telephone switching office. Most
cellular telephones transmit data in what is known as multiple frequency (MF) or
dual tone multiple frequency (DTMF) form. In accordance with the invention, a
cellular telephone, in addition to providing silent ring and auto answer,
includes at least a decoder for MF/DTMF signals.

A DTMF encoder/decoder handles numbers in base 10, i.e. the digits 0-9, as
opposed to binary numbers, the digits 0-1. In a preferred embodiment of the
invention, a cellular telephone includes a modem for transmitting binary data to
and from microprocessor 81 through transceiver 84. some commercially available
cellular telephones include an encoder, a decoder, and a modem. For such
telephones, only the software and the data stored in memory 82 need be modified
to implement the invention. Transmitting a pseudo-number, waiting for a request
for data, comparing data with stored data, and sending a code stored in memory
are tasks that are easily implemented in software whether microprocessor 81 has
a rich instruction set or a reduced instruction set.

An advantage of the invention over the prior art is the ability to encode a
subscriber's cellular telephone remotely. Because the telephone includes a
modem, data can be transferred over telephone lines to the subscriber's
telephone, for example to change security codes or to modify the programming
within the telephone. Not only is physical access not required but this
capability enables one to sell telephones through a national chain of stores and
activate the telephones remotely. Similarly, if a subscriber moves, the
subscriber's "home" cell can be changed remotely to the new location. The memory
in the cellular telephone need only include an EAROM (electrically alterable,
read-only memory).

FIG. 8 is a block diagram of a pre-pay service unit. unit 90 includes
microprocessor 91 connected to memory/mass storage 92 and line interface 93.
Memory/mass storage 92 contains the codes, account information, and tables for
translating incoming calls to the appropriate destination telephone number and
for monitoring the accounts of subscribers. Line interface 93 includes
appropriate circuitry for coupling land lines to microprocessor 91, encoding and
decoding MF/DTMF signals, and modems for transferring data to and from
subscribers. Printed circuit boards or cards are commercially available for
performing these functions and a array of cards is used in unit 90 for
connecting lines 96 to a public switching network. Lines 96 can be implemented
by wire, optical fiber, microwave links, or a cellular network. Line 94 is a
"WATS" or "800" line. More than one "800" number can be used, depending upon
loading.

A system incorporating the invention operates conventionally for billing, busy
signals, inadequate pre-paid balance, and the like. A distinct advantage of the
invention is that attempted theft of services is immediately detected because of
the data exchange between a subscriber's cellular telephone and the pre-pay
service unit. Referring to FIG. 4, for example, if someone obtained the actual
dial-in number is for telephone 20, the pre-pay service unit cannot be by-passed
because telephone 20 awaits a security code before proceeding. Without the code,
the call is terminated and is counted as suspect in telephone 20. In a preferred
embodiment of the invention a fixed number of suspect calls, e.g. three,
disables telephone 20 until the telephone is physically returned to the pre-pay
service provider for correction. Similarly, without the security code, a call
cannot be placed from telephone 20.

The invention thus provides a cellular telephone system for pre-paid subscribers
in which the system is transparent to existing telephone networks and can
monitor both outgoing and incoming calls without the need for dedicated lines at
an MTSO. Theft is detected as soon as an attempt is made and the call is
terminated. The invention can be implemented with commercially available
cellular telephones and switching equipment, requiring only software
modification.

Having thus described the invention, it will be apparent to those of skill in
the art that various modifications can be made within the scope of the
invention. For example, a rotating coding system can be used within the cellular
telephone. That is, for step 55 (FIG. 5), one of several possible codes is
transmitted for each outgoing call. Both the telephone and the pre-pay service
unit have the same table of codes and increment through the table in step.
Attempted thefts of service will very likely send the wrong code. The tables and
codes are different for each subscriber.

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