IMEI
(International Mobile Equipment Identifier)
A 15-digit number (composed of four parts) that uniquely identifies an individual wireless device. The IMEI is automatically transmitted by the phone when the network asks for it. A network operator might request the IMEI to determine if a device is in disrepair, stolen or to gather statistics on fraud or faults.
IMEI is most commonly used in GSM and WCDMA (UMTS) phones. It is embedded in the phone, not the SIM card. CDMA phones use a similar type of number called an ESN.
See: ESN
