271 lines
18 KiB
Plaintext
271 lines
18 KiB
Plaintext
A GUIDE TO CELLULAR PHREAKING
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--by Bernie S.
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The recent FBI/Secret Service cellular sting operation that culminated in the
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arrests of over 25 people in New York City confirms what many of us have
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suspected for quite some time: that cellular telephone fraud is widespread.
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The FBI estimates that cellular phone fraud costs system operators $3 million
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anually; with the average subscriber's airtime bill about $50 per month for 100
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minutes of usage, there could be over 2500 cellular pirates on the air if a
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pirate uses twice the normal amount of airtime. The term "pirate" rather than
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"phreak" is used here because the vast majority of illegitimate CMT users
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(Cellular Mobile Telephone) are only interested in stealing airtime, while
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phone phreaks are mainly interested in learning more about the telephone
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network through its manipulation.
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The six-month FBI investigation used "cooperative sources" who named
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fraudulent installers; then FBI agents posing as customers and installers used
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standard entrapment techniques to gather evidence against those allegedly
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involved. The FBI's press release statement that "Recent technological
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advances in computerized telephone switching equipment and billing systems were
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instrumental in...(their investigation)" is deliberately misleading. New York
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cellular carrier NYNEX merely supplied the FBI with its billing data to
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document the use of bogus and stolen ESN's & MIN's (Electronic Serial Numbers
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and Mobile Identification Numbers) discovered in the investigation. The Secret
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Service later became involved because the laws relating to the credit fraud
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being allegated are under their jurisdition.
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SAFE PHREAKING: In practice, cellular phreaking is very safe if one does
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their own tranceiver modifications, changes ESN's & MIN's regularly, and uses
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standard phone-phreak precautions. Indeed, FBI agent Greg Meecham has stated
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that fraudulently programmed CMT's are "anattributable, unbillable,
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untraceable and untappable." A cellular carrier will become aware of any bogus
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or stolen ESN's and MIN's used on its system within a month or so after their
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initial use once the subscriber or carrier who is assi gned those codes is
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billed and notifies them of the error. The home carrier will then change the
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legitimate subscriber's MIN in the MTSO (Mobile Telephone Switching Office) and
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arrange for a new NAM (Number Assignment Module, or ROM) to be installed in t
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hat subsciber's CMT transceiver. The MTSO maintains a database of all its
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valid ESN/MIN pairs, as well as a "negative verify" file on all known invalid
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numbers for the deadbeats and pirates in its area. The carrier may choose to
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leave certain fraudulent codes active to have any activity monitored, but as
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long as all parties at the receiving end of any phreaked calls become amnesiac
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to any inquiries, the phreak's identity will remain secret. If a phreak uses a
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different ESN & MIN every month, it'll be extremely difficult for the carrier
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to react in time to gather any information.
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As with any landline, inband signalling (i.e. 2600 Hz, MF tones, etc.) will
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work but can be easily detected by the ESS controlling that line. Since all
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cellular systems are in metropolitan areas, it's logical to assume that most
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cellular lines are on ESS . Although telco security may be aware of any
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blue-boxing, the links in their security chain stop at the MTSO. Moreover,
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since the MTSO selects outgoing landlines from a trunk group, a pen register at
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the CO would be useless for establishing any toll fr aud patterns.
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Because of cellular's inherent frequency-hopping nature, it is very difficult
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to track down a CMT using conventional radio direction-finding (DF) techniques,
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even if it's stationary. A small directional antenna aimed randomly at
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surrounding cell-site rep eaters with a TV antenna rotor will thoroughly
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confuse any DF attempts, although keeping calls as short as possible is always
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a good precaution. Locating a mobile CMT is virtually impossible. I was
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recently given a tour of an FCC monitoring van in Washi ngton DC, and was
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suprised to see how lacking in sophistication their onboard DF gear was. The
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only equipment available to readily locate a CMT transmitter is primarily used
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by the military and intelligence agencies, which couldn't care less about CMT
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fr aud unless it involved national security.
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EQUIPMENT: Most CMT's are actually two main pieces of equipment: the
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transceiver and control head. The transceiver (transmitter/receiver) is
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usually a nondescript metal box with three external connectors and contains
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sophisticated circuitry. There are usually two main circuit boards inside: an
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RF board with all the radio transmitting/receiving circuits, and a logic board
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with a microprocessor, A/D & D/A circuits, and control logic. The control head
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is a Touch-Tone telephone handset with an extended ke ypad, numeric or
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alphanumeric display, and volume and mic mute controls. It often has a
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seperate speaker mounted in the cradle for on-hook dialling and call-progress
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monitoring. Some CMT's have a speakerphone option that allows you to drive
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with both ha nds on the wheel by talking into a small microphone mounted near
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the vehicle's sun-visor, and listening to the cradle loudspeaker. This may
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seem to be the ultimate in laziness, but remember you could be maneuvering your
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five-speed through heavy traffic o n the exressway when the phone rings! The
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control head/cradle is usually bolted to the transmission hump by the drivers
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seat, and the transceiver is usually mounted in the trunk with a power cable
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connecting it to the car battery and ignition switch. A shielded control cable
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links this equipment together and allows data and audio to pass between them.
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Most first-generation CMT's used the AMPS bus, developed by AT&T, which
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specified a system of 36 parallel wires in a bulky control cable. Some
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manufactu rers later developed their own busses--Novatel's serial bus specifies
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a thin cable of just a few wires which is much easier to install in vehicles.
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For fixed use, a CMT may be powered by any 12-volt regulated DC power supply
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that can deliver at least 5 A mperes.
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Any would-be cellular phreak must first obtain a CMT. Used bargains abound
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in some cities, where many subscribers found they couldn't afford to pay their
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airtime bills after they bought their phone! First-generation E.F. Johnson
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transceivers are a good choice because they're easy to work on, use a uniquely
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effective diversity (dual-antenna) receiver, and use the AMPS control bus,
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which means that several manufacturers' control heads will work with it.
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Another good choice is Novatel's Aurora/150 model. It uses a proprietary
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parallel bus and control head, but costs less, is very rugged, and is also easy
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to work on. In addition, all Novatel CMT's have built-in diagnostics which
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allow (among other things) manual scanning of all 666 repeater output freque
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ncies--great entertainment when you're bored!
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ANTENNAS: A mobile cellular antenna is usually a short (less than a foot
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long) piece of stiff wire with a half-dozen or so turns in the middle, like a
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spring. The "spring" acts as a phasing coil in a 5/8-wave configuration. The
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antenna is mounted verti cally either through a hole in the vehicle's roof or
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at the top of the rear windshield using silicone adhesive with conductive
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plates on either side to pass RF energy right through the glass. It's not
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quite as efficient as a roof mount, but most folks pr efer not to drill a hole
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in their Mercedes. A 50-Ohm coaxial cable such as RG-58/U links the antenna to
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the transceiver with a male TNC-type UHF connector. A ceramic duplexer allows
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the transmitter and receiver to share the same antenna simultaneously. Mobile
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roof-mount antennas are designed to work with the ground plane provided by the
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vehicle's body, but for fixed use an "extended-feed" or voltage-fed coaxial
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antenna (which requires no ground plane) can be used if there's no tin roof on
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your house. A capped PVC pipe makes an ideal rooftop housing for this type of
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antenna, concealing it and making it weatherproof at the same time. As with
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any kind of antenna, the higher the better--but unless you're surrounded by
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tall steel buildings any height will probably do (provided you're within range
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of a cell-site repeater.) It should even work indoors if near a
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window--remember that cellular systems are designed to work primarily with
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inefficient antennas at ground-level. Yagi and corner-reflector antenna s are
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available for fixed use that provide very high gain and directivity. Antenna
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specialists Co. (216/791-7878) manufactures a broad line of cellular antennas.
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INTERFACING: Interfacing audio devices such as MF tone-generators to a CMT
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can be accomplished by coupling the device's output through an audio coupling
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transformer and capacitor across the control head's microphone wires. If it's
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available, a schematic diagram will show which CMT bus lines carry the transmit
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audio; coupling the signal there would be preferable. Acoustic modems can be
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interfaced acoustically, or by coupling the mic and speaker wires to those on
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the control head or to the appropriate bu s lines. Direct-connect modems,
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answering machines, regular and cordless telephones and other devices can be
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interfaced to a CMT through the AB1X cellular interface manufactured by
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Morrison & Dempsey Communications (818/993-0195). This compact $300 devi ce is
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a one-line PBX that connects between the tranceiver and control head and
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provides an RJ-11C jack that accepts ANY direct-connect telephone accessory.
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It recognizes Touch-Tone and pulse dialling, provides 1.0B equivalent ringing
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voltage, and generat es dial and busy tones when appropriate.
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ACCESS CODES: Every CMT manufactured has a unique ESN, which is an four-byte
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hexadecimal or 11-digit octal number in a ROM soldered directly to the logic
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board. It's supposed to be there for life and never removed. Some newer CMT's
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embed the ESN in a V LSI chip along with the unit's program code, which makes
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ESN modifications virtually impossible. The ESN is also imprinted on the
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receiver ID plate mounted on the outside housing. When converted to octal (11
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digits), the first three digits specify the C MT manufacturer, and the other 8
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identify the unit. Typical ESN's might be 13500014732 (octal) for a NEC brand
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CMT, and 8E01A7F6 (hexadecimal) for a Novatel. The other important chip is the
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NAM, which contains the MIN (NPA-XXX-XXXX), lock code (keeps th e kids from
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using it) and various model-specific and carrier-specific codes. Some newer
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CMT's have no NAM at all and use an EEPROM which allows a technician who knows
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the maintenance code to change NAM data through the control head keypad.
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Basically, when one attempts to make a CMT call the transceiver first
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automatically transmits its ESN & NAM data to the nearest cell-site repeater by
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means of the overhead data stream, or ODS. The ODS is a 10 kilobaud data
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channel that links the CMT's co mputer to the MTSO computer, which controls the
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phone's entire operation right down to its channel and RF output power. If the
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MTSO doesn't recognize the received ESN/MIN pair as valid, it returns a reorder
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signal and will not process the call. In most cities with cellular systems
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there are two carriers: the wireline operator (usually Bell or the local
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telco) and the non-wireline operator, an independant company. Both maintain
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their own MTSO and network of cell-site repeaters, and occupy seperate halve s
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of the cellular radio band. Non-wirelines operate on system A (channels 001 to
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333), and wirelines on system B (channels 334 to 666.)
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Custom-Calling features such as call-forwarding, call-waiting, and three-way
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calling are all standard with most cellular carriers, but the procedures for
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using them differ so it's best to call the carrier for more information.
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OBTAINING CODES: The most difficult task for cellular phreaks and pirates is
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obtaining usable ESN's and MIN's. One method involves having an accomplice who
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is employed at a CMT installation center. They will have a file on every CMT
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installed at that l ocation, including the ESN's & MIN's assigned to those
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subscribers. Using several codes from one source could focus attention there,
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however. Another method involves the help of an inside person at the cellular
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carrier's customer service or billing depa rtment, where many low-paid
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employees have access to thousands of valid ESN's & MIN's. The most
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sophisticated method requires interfacing a CMT's A/D circuitry to a personal
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computer, enabling one to literally pick valid codes out of thin air.
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PROGRAMMING THE CMT: Once a valid ESN/MIN pair is obtained, it must be
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programmed into the CMT's ROM'S. Some CMT manufacturers use different devices
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and memory maps, but most adhere to the AMPS 16-pin, 32 x 8 bit format. The
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most common ROM's are Signe tics 82S23 (open collector) and 82S123 (tri-state)
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or equivalents, but it's best to check the part numbers used in your unit. The
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existing ESN ROM should be carefully removed from the logic board using
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grounded desoldering tools and read using a NAM prog rammer' bit-editor mode.
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Any PROM programmer that is device-compatible can be used, but dedicated NAM
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programmers have built-in software which greatly simplifies the process. The
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ESN printed on the ID plate (if in decimal, convert to hex) should be foun d in
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memory and will be immediately followed by an 8-bit checksum determined by the
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8 least significant bits of the hex sum of the ESN's four bytes. The old ESN
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data (now copied into the NAM programmer's RAM) should be replaced with the new
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ESN and check sum. A new blank ROM of the same type should be inserted into
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the programmer and "burned." It would be advisable to solder a ZIF (Zero
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Insertion Force) DIP socket onto the logic board to accomodate the new ESN chip
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and any future versions.
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The NAM chip is usually already ZIF socketed on the logic board for easy
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replacement. It, too should be copied into the NAM burner's RAM and the old
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MIN replaced with the new one. The NAM checksum should also be updated to
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reflect the new data. Althoug h the carrier's system parameters must also be
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programmed into the NAM, they can be left the same if the NAM being changed had
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previously been on the carrier now to be used. All that needs to be changed in
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this case is the last four MIN digits and checks um (and maybe the exchange if
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they're using more than one.) An excellent write-up on NAM programming is
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available free of charge from Curtis Electro Devices (415/964-3846). Ask for
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the May '87 reprint from Cellular Business magazine. Bytek Corporation
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(305/994-3520) sells a good budget NAM programmer for about $500, and the
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operations manual (available seperately) explains in detail the memory maps,
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part numbers, and programming techniques for most CMT's on the market. This
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same unit is also capable o f programming many ESN chips using the bit-editor
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mode. Some carriers and their installation agents will provide NAM system
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parameters on request, and some CMT service facilities will provide NAM & ESN
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memory maps and schematics of specific CMT's for a p rice.
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One could eliminate the need for a NAM programmer altogether by programming
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and interfacing a personal computer to the CMT's ESN and NAM sockets. Another
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approach is to interface 2 banks of 8 hexadecimal thumbwheel switches to the
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sockets, although a com puter program would still be needed to determine the
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proper switch settings. Either of these two approaches will permit quick
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emulation of any CMT with an ESN & MIN of your choosing.
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ROAMING: Whenever a CMT is used in a cellular system other than the one
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indicated by the SID (System ID) code in its NAM, it is in the ROAM mode and
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the ROAM indicator on the control head will turn on. A CMT can roam in any
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system its home carrier has a roaming agreement with, and most carriers now
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have roaming agreements with each other. If there is no roaming agreement, the
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MTSO will transmit a recorded voice message to the CMT user with instructions
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to call the carrier (the only call the CMT will be able to make) and give his
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name, MIN, ESN, and American Express Card number. All roamed calls will then
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be completed by the MTSO and billed to the credit card account. Fortunately,
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this procedure is becoming less common as more roaming agreements are m ade.
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Usually, a carrier can only determine if a roamer came from a system with
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which it has a roaming agreement, not the creditworthiness of that roamer.
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Consequently, many carriers have been abused by roamers who've been denied
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service on their home system d ue to non-payment. Once the home carrier is
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billed for roaming services provided by the roamed carrier, it will notify same
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to add that ESN & MIN to their MTSO's "negative verify" file to prevent further
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abuses. Several independent companies are establi shing system software and
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data networks to allow Positive Roamer Verification (PRV) which will allow near
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real-time roamer validation by sharing data between carriers. Because of the
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many technical, financial, and political details that still need to be
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resolved, PRV systems will probably not be in place for at least two more
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years. In the meantime, even fictitious ESN's & MIN's can roam if they follow
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the standard format, although some carriers are sharing roamer data on a
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limited basis to curtail this .
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To call a roaming CMT, the caller must know which system that unit is in, and
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call that carrier's roaming number. Roaming numbers vary, but are usually in
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the format: (NPA)XXX-ROAM, where NPA is the carrier's area code and XXX is the
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MTSO exchange. Cal ling that number will return a dial or ready tone, after
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which the roamed CMT's full MIN should be entered in Touch-Tones. After a few
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seconds, the mobile unit will ring or the caller will hear a recording stating
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that the mobile unit is out of range. T elocator Publications (202/467-4770)
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publishes a nationwide roaming directory for travellers with cellular phones.
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Cellular Telephone technology offers phone phreaks complete safety by
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allowing miles of physical seperation from the wire pair, and by offering
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thousands of lines to choose from. In addition, all this is possible from just
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about any location, even from a car, boat, train, or aircraft. It is these
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characteristics that are attracting a sophisticated new breed of phone phreaks
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who will enjoy unprecedented convenience and security.
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