IMEI (International Mobile Equipment Identity) is a 15- or 17-digit code that uniquely identifies mobile phone sets. The IMEI code can enable a GSM (Global System for Mobile communication) or UMTS (Universal Mobile Telecommunications Service) network to prevent a misplaced or stolen phone from initiating calls.
In most mobile communications devices, the IMEI appears on the display when the user enters the character sequence *#06# (star-pound-zero-six-pound) into the keypad. The IMEI code may also be printed inside the battery compartment. When a phone set is lost or stolen, the owner can call the CEIR (Central Equipment Identity Register) and blacklist the device according to its IMEI number. After that action, the set will in most cases become useless, even if someone swaps out the unit's SIM card (subscriber identity module). However, although it is not an easy task, a skilled and determined cracker can sometimes change the IMEI number and use a stolen set to place calls.
Immediately after purchasing a mobile communications device, the owner should record the IMEI code in a secure place so that it can be quickly accessed in the event of loss or theft.