International Mobile Equipment Identity

International Mobile Equipment Identity

The International Mobile Equipment Identity (IMEI) is a number unique to every GSM and UMTS mobile phone. It is usually found printed on or underneath the phone's battery and can also be found by dialing the sequence *#06# into the phone.

The IMEI number is used by the GSM network to identify valid devices and therefore can be used to stop a stolen phone from accessing the network. For example, if a mobile phone is stolen, the owner can call his or her network provider and instruct them to "ban" the phone using its IMEI number. This renders the phone useless, regardless of whether the phone's SIM is changed.

Unlike the Electronic Serial Number or MEID of CDMA and other wireless networks, the IMEI is only used to identify the device, and has no permanent or semi-permanent relation to the subscriber. Instead, the subscriber is identified by transmission of an IMSI number, which is stored on a SIM card which can (in theory) be transferred to any handset. However, many network and security features are enabled by knowing the current device being used by a subscriber.

Structure of the IMEI

The IMEI is a 15-digit number which includes information on the origin, model, and serial number of the device. The model and origin comprise the initial 8-digit portion of the IMEI, known as the Type Allocation Code (TAC). The remainder of the IMEI is manufacturer-defined, with a Luhn check digit at the end (which is never transmitted).

As of 2004, the format of the IMEI is AA-BBBBBB-CCCCCC-D, although it may not always be displayed this way. This table explains what each part of the IMEI is.

AA BBBBBB CCCCCC D

Reporting Body Identifier, indicating the GSMA-approved group that allocated the model TAC code The remainder of the TAC Serial sequence of the model Luhn check digit of the entire number (or zero)

Prior to 2002, the TAC was 6 digits long and followed by a two-digit Final Assembly Code (FAC), which was a manufacturer-specific code indicating the location of the device's construction.

For example the code 35-209900-176148-1 tells us the following:

TAC: 352099 so it was issued by the BABT and has the allocation number 2099

FAC: 00 so it was numbered during the transition phase from the old format to the new format (described below)

SNR: 176148

CD: 1 so it is a GSM Phase 2 or higher

The format changed from April 1, 2004 when the Final Assembly Code ceased to exist and the Type Approval Code increases to eight digits in length and became known as the Type Allocation Code. From January 1, 2003 until this time the FAC for all phones was 00.

The Reporting Body Identifier is allocated by the Global Decimal Administrator; the first two digits must be decimal (ie less than 0xA0) for it to be an IMEI and not an MEID.

The new CDMA Mobile Equipment Identifier (MEID) uses the same basic format as the IMEI.

Retrieving IMEI information from a GSM device

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