Your Mobile Phone
When a mobile phone handset is made it is given a unique electronic serial number known as the International Mobile Equipment Identity (IMEI). This number is usually 14 to 18 digits long. The IMEI is usually found printed inside the battery compartment of the handset, except on iPhones where it is located on a pull-out tray. It can also be displayed on the screen of the phone by entering *#06# into the keypad. If your phone is new, the IMEI should also be labelled on the side of the box. Your network provider can also provide you with your IMEI. This number is extremely important as it identifies your phone in much the same way a chassis number is unique to a vehicle.
You can find your IMEI by entering *#06# into the keypad of your phone
When a phone is switched on, this unique IMEI number is transmitted and technology allows this number to be checked against a database of handsets that have been reported as lost or stolen to the mobile phone network provider's Equipment Identity Register (EIR). This EIR determines whether the handset can log onto the network to make and receive calls. This information is shared to ensure that a phone reported as lost or stolen to a network is 'blocked' for use on all networks, and will not work in the UK. It is illegal and a criminal offence to 'unblock' or offer to 'unblock' a phone.
A 'locked' phone is one that at the point of manufacturer has been tied to work on a single network as a commercial condition of use. That restriction can be lawfully removed as it is merely allowing the consumer to have a choice of provider. 'Unlocking' is regularly seen advertised in high street stores and is not illegal.
Your mobile phone number is linked to your Subscriber Identity Module (SIM) card. A similar check is made by the network to ensure that the SIM card has not been reported lost or stolen to your network.