IMEI is a number which is unique to every GSM mobile phone. It is usually found printed on or underneath the phone’s battery and warranty card. IMEI of any set 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 Authorities and instruct them to “block” the phone using its IMEI number. This renders the phone useless, regardless of whether the phone’s SIM is changed.