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The IMEI number is used by the GSM network to identify valid devices and therefore can be used for stopping a stolen phone from accessing the network in that country. For example, if a mobile phone is stolen, the owner can call his or her network provider and instruct them to "blacklist" the phone using its IMEI number. This renders the phone useless on that network and sometimes other networks too, whether or not the phone's SIM is changed.
The IMEI is only used for identifying 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 that 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.
IMEI blocking is not the only approach available for combating phone theft. For example, mobile operators in Singapore are not required by the regulator to implement phone blocking or tracing systems, IMEI-based or other. The regulator has expressed its doubts on the real effectiveness of this kind of system in the context of the mobile market in Singapore. Instead, mobile operators are encouraged to take measures such as the immediate suspension of service and the replacement of SIM cards in case of loss or theft.
There is a misunderstanding amongst some regulators that the existence of a formally-allocated IMEI number range for a GSM terminal implies that the terminal is approved or complies with regulatory requirements. This is not the case. The linkage between regulatory approval and IMEI allocation was removed in April, 2000, with the introduction of the European R&TTE; Directive. Since that date, IMEIs have been allocated by BABT (or one of several other regional administrators acting on behalf of the GSM Association) to legitimate GSM terminal manufacturers without the need to provide evidence of approval.
The IMEI number is not supposed to be easy to change, making the CEIR blacklisting effective. However this is not always the case: a phone's IMEI may be easy to change with special tools.
, the format of the IMEI is AA-BBBBBB-CCCCCC-D, although it may not always be displayed this way. The IMEISV drops the Luhn check digit in favour of an additional two digits for the Software Version Number (SVN), making the format AA-BBBBBB-CCCCCC-EE
Prior to 2002, the TAC was six digits long and was followed by a two-digit Final Assembly Code (FAC), which was a manufacturer-specific code indicating the location of the device's construction. From January 1, 2003 until that April 1, 2004, the FAC for all phones was 00. After April 1, 2004, the Final Assembly Code ceased to exist and the Type Allocation Code increased to eight digits in length.
In any of the above cases, the first two digits of the TAC are the Reporting Body Identifier, which identifies the GSMA-approved group that allocated the TAC. The RBI numbers are allocated by the Global Decimal Administrator. The first two digits are always decimal (i.e., less than 0xA0), allowing IMEI numbers to be distinguished from an MEID, which will always have 0xA0 or larger as its first two digits.
For example, the old style IMEI code 35-209900-176148-1 or IMEISV code 35-209900-176148-23 tells us the following:
TAC: 35-2099 - issued by the BABT (code 35) with the allocation number 2099 FAC: 00 - indicating the phone was made during the transition period when FACs were being removed. SNR: 176148 - uniquely identifying a unit of this model CD: 1 so it is a GSM Phase 2 or higher SVN: 23 - The "software version number" identifying the revision of the software installed on the phone. 99 is reserved.
By contrast, the new style IMEI code 49-015420-323751 has a 8-digit TAC of 49-015420.
The new CDMA Mobile Equipment Identifier (MEID) uses the same basic format as the IMEI.
According to the IMEI Allocation and Approval Guidelines,
The Check Digit shall be calculated according to Luhn formula (ISO/IEC 7812). (See GSM 02.16 / 3GPP 22.016). The Check Digit is a function of all other digits in the IMEI. The Software Version Number (SVN) of a mobile is not included in the calculation.The purpose of the Check Digit is to help guard against the possibility of incorrect entries to the CEIR and EIR equipment.
The presentation of the Check Digit both electronically and in printed form on the label and packaging is very important. Logistics (using bar-code reader) and EIR/CEIR administration cannot use the Check Digit unless it is printed outside of the packaging, and on the ME IMEI/Type Accreditation label.
The check digit is validated in three steps: # Starting from the right, double a digit every two digits (e.g., 7 → 14). # Sum the digits (e.g., 14 → 1 + 4). # Check if the sum is divisible by 10.
Conversely, one can calculate the IMEI by choosing the check digit that would give a sum divisible by 10. For the example IMEI 49015420323751?,
To make the sum divisible by 10, we set ? = 8, so the IMEI is 490154203237518.
Retrieving IMEI Information from an older Sony or Sony Ericsson handset can be done by entering these keys: * Right * Left Left * Left *
IMEI information on BlackBerry and on new Sony Ericsson devices can also be found by going to options, then status. On Android the IMEI information can be found under the "About Phone" menu option in the settings menu.
This text is licensed under the Creative Commons CC-BY-SA License. This text was originally published on Wikipedia and was developed by the Wikipedia community.
