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 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.
As of 2004, 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
|Reporting Body Identifier, indicating the GSMA-approved group that allocated the model TAC||The remainder of the TAC||Serial sequence of the model||Luhn check digit of the entire number (or zero)||Software Version Number (SVN).|
For example, the IMEI code 35-209900-176148-1 or IMEISV code 35-209900-176148-23 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 - 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.
The format changed as of April 1, 2004, when the Final Assembly Code ceased to exist and the Type Approval Code increased to eight digits in length and became known as the Type Allocation Code. From January 1, 2003 until that time the FAC for all phones was 00.
The new CDMA Mobile Equipment Identifier (MEID) uses the same basic format as the IMEI.
Retrieving IMEI Information from an older Sony or Sony Ericsson handset can be done by entering these keys: Right * Left Left * Left * (Other service menu items will be presented with this key combination).
The IMEI information can be retrieved from most older Nokia mobile phones by pressing *#92702689# (*#WAR0ANTY#); this opens the warranty menu in which the first item is the serial number (the IMEI). The warranty menu also shows other information, such as the date the phone was made and the life timer of the phone.
The IMEI can frequently be displayed through phone menus, under a section titled "System Information", "Device", "Phone Info" or something similar. Many phones also have the IMEI listed on a label in the battery compartment.
On refurbished phones, the IMEI may be different for the software and the actual phone itself. You can check this by looking behind the phone where the battery is placed (phone IMEI) and by pressing *#06# on your phone (software IMEI). This is because refurbished phones are often fitted with a housing from another phone.
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 (acting on behalf of the GSM Association) to legitimate GSM terminal manufacturers without the need to provide evidence of approval.
Other countries use different approaches when dealing with 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.
When mobile equipment is stolen or lost, the operator or owner will typically contact the Central Equipment Identity Register (CEIR), which blacklists the device in all operator switches so that it will, in effect, become unusable, making theft of mobile equipment a useless business.
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 and some operators may even flatly ignore the CEIR blacklist.
The last number of the IMEI is a check digit calculated using the Luhn algorithm.
According to the IMEI Allocation and Approval Guidelines,
The Check Digit is calculated according to Luhn formula (ISO/IEC 7812). See GSM 02.16 / 3GPP 22.016. The Check Digit shall not be transmitted to the network. 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 [registries].
The presentation of the Check Digit (CD), 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 CD unless it is printed outside of the packaging, and on the ME IMEI/Type Accreditation label.
The check digit shall always be transmitted to the network as "0".
The check digit is validated in three steps:
Conversely, one can calculate the IMEI by choosing the check digit that would give a sum divisible by 10. For the example IMEI 49015420323751?,
|Double every other||4||18||0||2||5||8||2||0||3||4||3||14||5||2||?|
|Sum digits||4 + (1 + 8) + 0 + 2 + 5 + 8 + 2 + 0 + 3 + 4 + 3 + (1 + 4) + 5 + 2 + ? = 52 + ?|
To make the sum divisible by 10, we set ? = 8, so the IMEI is 490154203237518.