Cellular fraud prevention using selective roaming

A method of preventing roaming fraud in cellular telephone systems using different levels of roaming privileges for individual subscribers. When the subscriber initiates a call in a foreign service area that exceeds their roaming privileges, an authentication method is used to verify the identity of the roaming subscriber.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates in general to a method of preventing cellular 
telephone fraud, and more specifically to a method of preventing cellular 
phone fraud using a pre-authorization technique for subscriber roaming 
privileges. 
2. Description of Related Art 
Cellular telephones combine the mobility of the radio link and the 
world-wide land telephone network to provide a communication link to any 
other telephone in the world. However, as cellular phones have become more 
prevalent throughout the country, fraud has become a major problem. 
Cellular fraud robs service providers of hundreds of millions of dollars 
every year. Like all crimes, there are several varieties of cellular 
fraud, including "cloning." 
Cloning fraud, which occurs when a legitimate subscriber's mobile 
identification number/electronic serial number (MIN/ESN) combination is 
used for illegal purposes, is among the most sophisticated and difficult 
forms of fraud to prevent. Often, the pirate will use simple electronic 
devices to "capture" the legitimate MIN/ESN combination during its 
transmission by radio frequency (RF). In these cases, the legitimate 
subscriber often does not know fraud is being committed with his or her 
MIN/ESN combination until they receive their bill. This is currently the 
most popular method of gaining illegal access to a cellular system, 
because the legitimacy of the stolen MIN/ESN combinations makes cloning 
difficult to catch. 
Often, cloning fraud occurs outside of the home area of the subscriber. 
Once the MIN/ESN information has been cloned, the MIN/ESN combination is 
valid for access to the cellular telephone system anywhere. Roamer fraud 
is committed by a local thief using a MIN/ESN imported from another 
service area, and thus not representing a true roaming subscriber. The 
exploited MIN/ESN is usually gathered through the use of a MIN/ESN reader 
in a home service area for the cellular phone. 
There are certain steps that can be taken to prevent cloning fraud. For 
example, U.S. Pat. No. 5,249,230 discloses a "challenge-response" system, 
wherein the cellular system "challenges" a cellular phone subscriber prior 
to granting access. The subscriber must manually "respond" to the 
challenge by entering a Personal Identification Number (PIN) or other code 
that is then verified against a centralized database maintained by the 
cellular system. However, this method is not attractive to most 
subscribers since it requires additional work and inconvenience. 
In another example, U.S. Pat. No. 5,239,294 discloses a technique that 
encrypts a PIN that is permanently programmed into the cellular phone, 
wherein the PIN is automatically transmitted to the cellular network 
during call setup. However, this method is expensive to implement, and is 
still subject to cloning, since the cloner need not discriminate between 
encrypted and unencrypted PINs to merely repeat a sequence of numbers 
observed being transmitting to the cellular system. 
Call pattern monitoring is another method used to prevent cellular phone 
fraud. This method works because most subscribers call only a specific set 
of phone numbers. When a call for a subscriber falls outside of that usual 
group, a challenge-response action can be initiated by the service 
provider. However, for new subscribers who have no previous calling 
history, or for subscribers who have a wide range of calling patterns, 
this method is ineffective. 
It can be seen, then, that there is a need for more effective techniques 
for preventing cellular phone fraud. Furthermore, such techniques must be 
easy and inexpensive to implement, and must not put unacceptable demands 
on subscribers. 
SUMMARY OF THE INVENTION 
To overcome the limitations in the prior art described above, and to 
overcome other limitations that will become apparent upon reading and 
understanding the present specification, the present invention discloses a 
powerful and highly productive method for preventing roaming fraud. The 
present invention uses different levels of roaming privileges for 
individual subscribers. The present invention also provides a method for 
authenticating subscribers when the subscriber initiates a call in a 
foreign service area that exceeds their roaming privileges. 
One object of the present invention is to prevent cellular fraud by use of 
authentication techniques for roaming subscribers. Another object of the 
present invention is to make the authentication technique as convenient 
and inexpensive to the subscribers as possible. 
These and various other advantages and features of novelty which 
characterize the invention are pointed out with particularity in the 
claims annexed hereto and form a part hereof. However, for a better 
understanding of the invention, its advantages, and the objects obtained 
by its use, reference should be made to the drawings which form a further 
part hereof, and to accompanying descriptive matter, in which there is 
illustrated and described specific examples of an apparatus in accordance 
with the invention.

DETAILED DESCRIPTION OF THE INVENTION 
In the following description of the preferred embodiment, reference is made 
to the accompanying drawings which form a part hereof, and in which is 
shown by way of illustration the specific embodiment in which the 
invention may be practiced. It is to be understood that other embodiments 
may be utilized as structural changes may be made without departing from 
the scope of the present invention. 
The present invention provides a method for preventing cellular fraud by 
restricting roaming privileges to cellular telephone subscribers, and 
requiring authentication from those subscribers when the subscriber 
initiates a call that exceeds their roaming privileges. 
FIG. 1 is a diagram of a typical cellular telephone system 10. The basic 
concept of the cellular telephone system 10 is to increase the 
availability of mobile telephone service, which always has been a scarce 
luxury, by reducing the area covered by a transceiver 12 by reducing the 
power of transmission. In this way, concentrated areas of population can 
have more transceivers 12, and thus more channels, because each 
transceiver 12 handles a given number of conversations. In addition, 
because the transceivers 12 cover less area, the same frequency can be 
re-used in a common geographical area. 
Within a cellular telephone system 10, a service area is divided into 
regions called cells 14, each of which has the necessary equipment to 
switch, transmit, and receive calls to and from any cellular phone 16 
located in the cell. A transceiver 12 in each cell 14 can transmit and 
receive on a plurality of FM channels in a specified frequency range 
simultaneously. 
Each cell 14 has at least one setup channel dedicated to signaling between 
the cell 14 and cellular phones 16 within the cell 14. The remaining 
channels are used for conversation. Each channel may be re-used between 
cells 14, so long as the re-use factor avoids interference by allowing 
channel re-use in cells 14 that are not adjacent to one another, and are 
far enough apart to avoid excessive interference. Thus, a system 10 with a 
relatively small number of subscribers can use large cells 14, and as 
demand grows, the cells 14 are divided into smaller ones. 
A cellular telephone 16 consists of a control unit, a transceiver, and 
appropriate antennas. The transceiver contains circuits that can tune to 
any of the channels assigned to the cellular system 10. Each cellular 
telephone 16 has a unique electronic serial number (ESN). Additionally, 
each cellular telephone 16 is assigned a 10-digit telephone number, known 
as a mobile identification number (MIN). 
Cells 14 are interconnected and controlled by a central Mobile 
Telecommunications Switching Office (MTSO) 18, which is basically a 
telephone switching office as far as hardware is concerned, but includes a 
substantial amount of additional digital equipment programmed for cellular 
control. The MTSO 18 not only connects the system 10 to the land telephone 
network, but also records call information for billing purposes. 
The cellular telephone system 10 of FIG. 1 is made up of a plurality of 
service areas 20, 22, 24, and 26 that may (or may not) be operated by 
different cellular service providers or carriers. Generally, each of the 
different service areas 20, 22, 24, and 26, is controlled by a 
corresponding local MTSO 18, 28, 30, and 32, respectively, and each of the 
service areas 20, 22, 24, and 26 is identified by a System Identification 
Number (SID). All cellular phones store an SID entry in their memory that 
identifies the "home" service area for the cellular phone 16. For example, 
as a cellular phone 16 travels from its "home" service area 20 to another 
service area 22, the "foreign" service area 22 provides the cellular 
services to the cellular phone 16, which is then known as a "roamer" in 
the foreign service area 22. 
Generally, agreements between service providers allow for unrestricted 
roaming by their respective subscribers. Charges incurred by the roamer 
are transmitted back to the "home" service provider, which pays the 
"foreign" service provider and then, in turn, bills the subscriber. Of 
course, if the roamer is fraudulent, the "home" service provider cannot 
charge the subscriber and thus must absorb the loss itself. The losses 
from roaming fraud are estimated to be in the tens of millions of dollars 
each year. The fact that roamer fraud causes the "home" service provider 
to lose money, rather than just providing free service, is a powerful 
impetus behind the development of the present invention. 
In the prior art, all subscribers default to having roaming privileges, 
unless a roamer restriction is specifically requested. A blanket roaming 
privilege extends to anywhere a valid carrier-to-carrier roamer agreement 
exists in the U.S., Canada, and parts of Mexico. These roamer privileges 
are granted even to those subscribers that are safety or security 
conscious and who rarely use the phone, much less roam from their home 
service area. 
In the present invention, policy changes are instituted to restrict roaming 
privileges, and automated systems are provided to authenticate roaming 
subscribers. As a result, only those subscribers with an expressed need 
for roaming privileges are granted such privileges. Furthermore, depending 
on the restrictions in place for the subscriber, automated authentication 
may occur to verify the identity of the roaming subscriber. 
The present invention identifies the subscriber's specific individual 
roaming needs and provides automated authentication controls to create 
easy access to roaming, yet reduces overall exposure to roaming fraud. 
Under the present invention, seamless roaming is available for all valid 
subscribers who have the need for such roaming. In fact, seamless roaming 
is enhanced due to a probable reduction in the need for temporary 
suspension of roaming privileges on a market-by-market basis due to 
fraudulent use. 
Although the percentage is different in each market, preliminary evidence 
suggests that the majority of subscribers never roam from their home 
service area. Of those subscribers who occasionally roam, it is estimated 
that 75% to 85% limit their roaming to contiguous service areas or a 
regional service area close to their home service area. This leaves a mere 
5% to 10% of subscribers who roam to distant locations within North 
America. The present invention customizes roaming policies to better 
reflect roaming demographics and institutes automated authentication when 
necessary to better cope with a serious and growing roaming fraud problem. 
The first step in implementing the present invention is to collect 
information reflecting the demographics of roaming subscribers. Billing 
information obtained from the MTSO 18 contains exact data on which 
subscribers roam, where they roam to, and how often they roam. This 
information can be extracted, collected, and analyzed using a computer 
system. Once the information has been analyzed, the service provider can 
differentiate roamer treatment and status on a custom basis to meet each 
subscriber's unique needs. 
In the present invention, some subscribers are prevented from roaming, 
possibly due to past fraudulent use of the MIN/ESN of the cellular phone 
16, or because of bad credit histories, or because of some other reason. 
Other subscribers with no roaming history may require authentication prior 
to being granted roaming privileges in selected foreign service areas. 
Still other subscribers may be frequent roamers with an established credit 
history and thus can be allowed to roam everywhere in North America, 
without the need for additional authentication. Less frequent roaming 
subscribers may be allowed to roam in specific service areas across North 
America. Finally, other subscribers may be only allowed to roam in foreign 
service areas contiguous to their home service area. 
As a result of the above definitions, a large number of subscribers may be 
required to periodically authenticate while roaming in foreign service 
areas, in accordance with the teachings of the present invention. For 
example, if a subscriber from service area 20 without sufficient roaming 
privileges uses their cellular phone 16 in a foreign service area 22, then 
the MTSO 28 in service area 22 recognizes, from the MIN of the cellular 
phone 16, that the cellular phone 16 is a roamer. The MTSO 28 identifies 
the MTSO 18 of the home service area 20 using the SID of the cellular 
phone 16, and transmits a message to the MTSO 18 in the home service area 
20 requesting validation for the roaming cellular phone 16, generally 
using an SS7 or IS-41 connection. 
The MTSO 18 passes the validation request to a service node 34 connected 
thereto, wherein the service node 34 comprises a computer that may have 
fixed and/or removable data storage devices 36 and 38, operator positions 
or terminals 40, and interactive voice response units (IVRUs) 42 attached 
thereto. Those skilled in the art will recognize that any combination of 
the above components, or any number of different components, peripherals, 
and other devices, may be used with the service node 34. 
The use of such service nodes 34 attached to MTSOs or COs (central offices) 
is well known in the art for use with applications such as voice mail, 
voice recognition, cable TV pay-per-view, etc. Of course, in the present 
invention, the service node 34 is specially configured and programmed for 
use in authenticating roaming cellular phones 16. 
The present invention is generally implemented using one or more computer 
programs executed by the service node 34. Generally, the computer programs 
are all tangibly embodied in a computer-readable medium, e.g., one or more 
of the fixed and/or removable data storage devices 36 and 38, including 
their associated media such as diskettes, tapes, etc. Moreover, the 
computer programs executed by the service node 34 are all comprised of 
instructions which, when read and executed by the service node 34, causes 
the service node 34 to perform the steps necessary to implement and/or use 
the present invention. The computer programs may be loaded from the data 
storage devices 36 and/or 38 into the memory of the service node 34 for 
use during actual operations of the authentication method. 
In accordance with the instructions of the computer programs, the service 
node 34 checks to see if the cellular phone 16 has sufficient roaming 
privileges. The service node 34 checks a database stored in the data 
storage units 36 and 38 to determine the roaming privileges of the 
cellular phone 16. Preferably, the database comprises both a Home Locator 
Register (HLR) 36 for storing roaming information (roaming privileges and 
identifying information) for subscribers of the home service area 20 and a 
Visitor Locator Register (VLR) 38 for storing roaming information 
(validation and validation period) for subscribers of the foreign service 
areas 22, 24, or 26, that are currently roaming in the home service area 
20. 
If a check of the Home Locator Register 36 in the service node 34 indicates 
that the cellular phone 16 has no roaming privileges, then the service 
node 34 responds with a denial signal to the MTSO 28 in the foreign 
service area 22. This denial signal instructs the foreign service area 22 
to deny cellular services to the roaming cellular phone 16, with an 
implicit understanding that the home service area 20 will not absorb any 
losses if the foreign service area 22 ignores the denial. 
If a check of the Home Locator Register in the service node 34 indicates 
that the cellular phone 16 has sufficient roaming privileges, then the 
service node 34 responds with an authorization signal to the MTSO 28 in 
the foreign service area 22. This authorization signal authorizes the 
foreign service area 22 to provide roaming services to the roaming 
cellular phone 16, with an implicit understanding that the home service 
area 20 will absorb any losses if the roaming cellular phone 16 has been 
cloned. 
If a check of the Home Locator Register 36 in the service node 34 indicates 
that the cellular phone 16 does not have sufficient roaming privileges, 
but is not prevented from roaming, then the service node 34 responds with 
an authentication request signal to the MTSO 28 in the foreign service 
area 22. It is envisioned that each service area 20, 22, 24, and 26, has 
its own service node 34, 44, 46, and 48, respectively. The MTSO 28 in the 
foreign service area 22 passes the authentication request signal to the 
service node 44 connected thereto, wherein the service node 44 in the 
foreign service area 22 performs an authentication method using 
identification information received from the service node 34 in the home 
service area to determine whether the cellular phone 16 has been cloned. 
In the preferred embodiment, one or more authentication methods could be 
used, including tiered levels of authentication if the subscriber fails an 
initial authentication attempt, as described in more detail below. 
If the roaming cellular phone 16 successfully authenticates, then, by 
agreement between the service providers 20 and 22, no further 
authentication may be required for the roaming cellular phone 16 for a 
specified period of time, e.g., 24 hours or 48 hours or some other period. 
Generally, this information is stored in the Visitor Locator Register of 
the service node 44 in the foreign service area 22, so that subsequent 
call attempts by the roaming cellular phone 16 within the specific period 
do not require communication with the service node 34 in the home service 
area 20, until after the expiration of the validation period. 
If the roaming cellular phone 16 does not successfully authenticate, a next 
higher level of a multi-level authentication method could be used. Failing 
all attempts to authenticate the roaming cellular phone 16 would result in 
the denial of roaming cellular services by the foreign service area 22. 
Note that the use of an authentication method only occurs if the roaming 
cellular phone 16 is restricted, at some level, from roaming by the home 
service area 20. As a result, the present invention minimizes the 
inconveniences to subscribers. On the other hand, if the subscriber roams 
more frequently, the roaming restrictions can be lessened or the level of 
roaming privileges increased simply by making a request to the service 
provider for their home service area 20. 
FIGS. 2A-2F together are a flowchart that illustrates the logic performed 
by the service node 34 to validate roaming subscribers in accordance with 
the present invention. Those skilled in the art will recognize that 
service nodes 44, 46, and 48 perform similar functions. 
Block 50 represents the service node 34 in the home service area 20 
receiving one of four messages via the MTSO 18: (1) a request to validate 
a roaming cellular phone 16 in the home service area 20; (2) a request to 
validate a roaming cellular phone in a foreign service area 22, 24, or 26; 
(3) a response from a foreign service area 22, 24, or 26, to a request 
made by the service node 34 to validate the roaming cellular phone 16 in 
the home service area 20; or (4) a call forwarding response for the 
roaming cellular phone 16 from a foreign service area 22, 24, or 26, to a 
request made by the service node 34 to authenticate the roaming cellular 
phone 16 in the foreign service area 22, 24, or 26. 
Those skilled in the art will recognize that the service node 34 could 
communicate with the MTSOs or service nodes in other service areas via the 
MTSO 18, using SS7 signalling or IS41 protocols or some other protocol or 
signalling method. Alternatively, those skilled in the art will recognize 
that the service node 34 could be directly connected with the MTSOs or 
service nodes in other service areas. 
Block 52 is a decision block that represents the service node 34 
determining whether the message is a request to validate a roaming 
cellular phone 16 in the home service area 20. If so, control transfers to 
FIG. 2B via "A"; otherwise control transfers to block 54. 
Block 54 is a decision block that represents the service node 34 
determining whether the message is a request for authorization from a 
foreign service area 22, 24, or 26 for the roaming cellular phone 16 in 
the foreign service area 22, 24, or 26. If so, control transfers to FIG. 
2C via "B"; otherwise control transfers to block 56. 
Block 56 is a decision block that represents the service node 34 
determining whether the message is a response from a foreign service area 
22, 24, or 26, to a previous request made by the service node 34 to 
authorize cellular services for the roaming cellular phone 16 in the home 
service area 20. If so, control transfers to FIG. 2D via "C"; otherwise 
control transfers to block 58. 
Block 58 is a decision block that represents the service node 34 
determining whether the message is a call forward from a foreign service 
area 22, 24, or 26, in response to a previous request for the same made by 
the service node 34 to authorize cellular services for the roaming 
cellular phone 16 in the foreign service area 22, 24, or 26. If so, 
control transfers to FIG. 2E via "D"; otherwise control transfers to block 
50. 
Referring now to FIG. 2B, block 60 is a decision block that represents the 
service node 34 determining whether the roaming cellular phone 16 is 
present in the Visitor Locator Register 38, i.e., has been previously 
authorized for roaming in the home service area 20. If so, control 
transfers to block 62; otherwise control transfers to block 66. Block 62 
is a decision block that represents the service node 34 determining 
whether the authorization period for the roaming cellular phone 16 in the 
Visitor Locator Register 38 has expired. If not, control transfers to 
block 64; otherwise control transfers to block 66. Block 64 represents the 
service node 34 transmitting a message to the MTSO 18 to complete the call 
for the roaming cellular phone 16 in the home service area 20, and then 
control transfers to block 70. Block 66 represents the service node 34 
identifying the foreign service area 22, 24, or 26 that is the "home" 
service area for the cellular phone 16, using the SID received from the 
cellular phone 16. Block 68 represents the service node 34 transmitting a 
message to the service node 36, 38, or 40, in the identified foreign 
service area 22, 24, or 26, requesting authorization for providing 
cellular services for the roaming cellular phone 16 in the home service 
area 20. Finally, block 70 returns to FIG. 2A. 
Referring now to FIG. 2C, block 72 represents the service node 34 
retrieving a data record from the Home Locator Register 36 associated with 
the roaming cellular phone 16 that contains the roaming privileges or 
restrictions for the cellular phone 16 and comparing the data record to 
the SID of the foreign service area 22, 24, or 26, where the roaming 
cellular phone 16 is located. Block 74 is a decision block that represents 
the service node 34 determining, from the data record, whether the roaming 
cellular phone 16 is authorized to roam in the foreign service area 22, 
24, or 26. If not, then control transfers to block 76, which represents 
the service node 34 responding to the request from the foreign service 
area 22, 24, or 26, with a denial signal. Otherwise, control transfers to 
block 78. Block 78 is a decision block that represents the service node 34 
determining, from the data record, whether the roaming cellular phone 16 
is allowed to roam in the foreign service area 22, 24, or 26, but only 
after authentication. If not, then control transfers to block 80, which 
represents the service node 34 responding to request from the foreign 
service area 22, 24, or 26, with an authorization signal. Otherwise, 
control transfers to block 82. Block 82 is a decision block that 
represents the service node 34 determining, from records in its database, 
whether the foreign service area 22, 24, or 26 has the capability to 
authenticate the roaming cellular phone 16. If not, control transfers to 
block 84, which represents the service node 34 responding to the foreign 
service area 22, 24, or 26, with a call forwarding request, so that the 
service node 34 can perform the authentication itself. Otherwise, control 
transfers to block 86. Block 86 represents the service node 34 responding 
to request from the foreign service area 22, 24, or 26, with an 
authentication request, including one or more authentication data fields. 
Finally, block 88 returns to FIG. 2A. 
As indicated above, it is envisioned that most, if not all, of the foreign 
service areas 22, 24, or 26 will have a service node 44, 46, or 48, 
respectively, that can perform the authentication steps in a manner 
similar to service node 34. On the other hand, some foreign service areas 
may not have service nodes for performing the authentication steps. 
Therefore, it is envisioned that the authentication steps for a roaming 
cellular phone 16 in another service area could, in fact, be performed by 
the service node 34 in the home service area 20 via call forwarding. 
For example, if authentication were required, but the foreign service area 
did not have a service node to perform the authentication method, then the 
service node 34 would respond to the request for validation with a request 
for the foreign service area to call forward the roaming cellular phone 16 
into an interactive voice response unit 42 coupled to the service node 34 
of the home service area 20. The service node 34 could then perform the 
necessary authentication steps before responding to the foreign service 
area with an authorization signal or a denial signal. Further, the service 
node 34 could also call forward the roaming cellular phone 16 to their 
dialed phone number for seamless service. Alternatively, the service node 
34 could, through its interactive voice response unit 42, merely instruct 
the roaming cellular phone 16 that is now authorized to roam in the 
foreign service area for a specified authorization period, and should 
re-dial the desired phone number. 
Referring now to FIG. 2D, block 90 is a decision block that represents the 
service node 34 determining whether the response is an authorization 
signal for roaming by the cellular phone 16 from the foreign service area 
22, 24, or 26. If so, control transfers to block 92, which represents the 
service node 34 updating its Visitor Locator Register 38 with the 
authorization and the authorization period and then block 94, which 
represents the service node 34 returning a response to the MTSO 18 to 
allow the call to be completed by the roaming cellular phone 16. 
Otherwise, control transfers to block 96. Block 96 is a decision block 
that represents the service node 34 determining whether the response is a 
denial signal for roaming by the cellular phone 16 from foreign service 
area 22, 24, or 26. If so, control transfers to block 98, which represents 
the service node 34 returning a response to the MTSO 18 that prevents the 
call by the roaming cellular phone 16 from being completed. Otherwise, 
control transfers to block 100. Block 100 is a decision block that 
represents the service node 34 determining whether the response is a "call 
forward" request by the foreign service area 22, 24, or 26. If so, control 
transfers to block 102, which represents the service node 34 returning a 
response to the MTSO 18 that call forwards the roaming cellular phone 16 
to a number indicated by the foreign service area 22, 24, or 26. 
Otherwise, control transfers to block 104. Block 104 is a decision block 
that represents the service node 34 determining whether the response is an 
authentication request by the foreign service area 22, 24, or 26, 
indicating that authentication is required for the roaming cellular phone 
16. If so, control transfers to FIG. 2F via "E"; otherwise, control 
transfers to block 106. Finally, block 106 returns to FIG. 2A. 
Referring to FIG. 2E, these steps refer to an authentication method 
performed for a roaming cellular phone 16 in a foreign service area 22, 
24, or 26. In this case, the roaming cellular phone 16 has been 
call-forwarded to the service node 34 for authentication, because the 
foreign service area 22, 24, or 26 lacks the capability to perform the 
authentication method. Block 108 represents the service node 34 retrieving 
the authentication data from the Home Locator Register 36 and performing 
the authentication method using the authentication data. Generally, the 
Home Locator Register 36 will contain one or more different data items 
therein for use with one or more authentication methods. In one example, 
an authentication data field received from the foreign service area 22, 
24, or 26 may contain a PIN for the roaming cellular phone 16 and the 
service node 34 couples the call to its interactive voice response unit 
42, requests manual entry of the PIN, and then waits for a correct 
response indicating authentication. In another example, the authentication 
data may contain other identifying information, e.g., the subscriber's 
social security number or the subscriber's mother's maiden name or other 
identifying data. Such other identifying information may be used in place 
of the PIN, or may be used in a tiered authentication method in 
conjunction with the failure of roaming cellular phone 16 to enter a 
correct PIN. Using the identifying information, the service node 34 
couples the call to the operator position 40, wherein an operator queries 
the subscriber across a voice channel in an attempt to authenticate their 
identity. If such attempts are successful, then the operator at the 
operator position 40 so informs the service node 34 via data entry into 
the service node 34. Of course, those skilled in the art will recognize 
that any number of different authentication methods could be used without 
departing from the scope of the present invention. Indeed, the present 
invention is capable of implementing any number of different types of 
authentication. Block 110 is a decision block that represents the service 
node 34 determining whether the roaming cellular phone 16 was 
authenticated. If not, control transfers to block 112, which represents 
the service node 34 returning a denial signal to the foreign service area 
22, 24, or 26. Otherwise, control transfers to block 114, which represents 
the service node 34 returning a authorization signal to the foreign 
service area 22, 24, or 26. Finally, block 116 returns to FIG. 2A. 
Referring to FIG. 2F, these steps refer to an authentication method 
performed for a roaming cellular phone 16 in the home service area 20, in 
response to a response from a foreign service area 22, 24, or 26. 
Generally, the response from the foreign service area 22, 24, or 26, will 
contain one or more data fields for use with one or more authentication 
methods, as described above. Block 120 is a decision block that represents 
the service node 34 determining whether the roaming cellular phone 16 was 
authenticated. If so, control transfers to block 122, which represents the 
service node 34 updating its Visitor Locator Register 38 with the 
authorization and the authorization period, and then to block 124, which 
represents the service node 34 transmitting a message to the MTSO 18 that 
allows the call to be completed by the roaming cellular phone 16. 
Otherwise, control transfers to block 126, which represents the service 
node 34 transmitting a message to the MTSO 18 that prevents the call from 
being completed by the roaming cellular phone 16. Finally, block 128 
returns to FIG. 2D. 
The foregoing description of the preferred embodiment of the invention has 
been presented for the purposes of illustration and description. It is not 
intended to be exhaustive or to limit the invention to the precise form 
disclosed. Many modifications and variations are possible in light of the 
above teaching. It is intended that the scope of the invention be limited 
not with this detailed description, but rather by the claims appended 
hereto.