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Understanding that and trying to look innocent, people often implement another
method available in any country with GSM coverage. They buy a few anonymous SIM cards and replace
them from time to time. Now, being under impression they are safe, they talk freely doing
sometimes a terrible mistake.
Interception equipment connected to switches of GSM network
provider (so called "Lawful Interception") almost
never satisfies with tracking targets by identities of their
SIM cards (IMSI). It also monitors identity of GSM handsets
(IMEI). So, to be untraceable, both the SIM card and the handset
should be changed together.
It is Siemens cellular mobile phones we have modified to turn those
into untraceable device. Every time you replace SIM card the phone automatically
will change its IMEI number. The IMEI numbers are produced by the phone randomly
and will never be repeated. Interception of conversations made or received by such
a phone becomes an impossible mission.

Understanding of IMEI (International Mobile
Equipment Identity)
IMEI stands for International Mobile Equipment
Identity. The IMEI is a unique 15-digit code used to identify
an individual GSM mobile telephone to a mobile network. The
IMEI can be displayed on most phones by dialing the code
*#06#. It is also usually printed on the compliance plate
under the battery. The numerical format of the IMEI code
is: 111111-22-333333-4. This format will be in place until
April 1st 2004.

- TAC: type approval code
- FAC : final assembly code
- SNR: serial number
- CD: check digit
The TAC (Type Approval Code) is formed by the first six digits of the
IMEI. This code identifies the country in which type approval was sought for
the phone, as well as the approval number.
NOTE: From 1st April 2004 the TAC will be the abbreviation for Type Allocation Code.
The FAC (Final Assembly Code) identifies the company that produced the mobile phone (for instance: Sony-Ericsson or Nokia).
The SNR (Serial Number) is a six digit code, which has been uniquely
assigned to the specific type of handset. The CD (Check Digit) is used to check
the IMEI for its validity for Phase 2 and Phase 2+ handsets. Phase 1 GSM handsets,
however, always have zero (0) as check digit.
NOTE: From 1st January 2003 a new IMEI allocation procedure is in place. The changes relate to the format of the IMEI; the Final Assembly Code (FAC) will be obsolete and be set to 00 for the period from 1st January 2003 until 1st April 2004. After that the FAC will be obsolete, and the TAC will be eight digits in stead of six digits. The numerical format of the IMEI code will then be: 11111111-222222-3:

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