An International Mobile Equipment Identity (IMEI) number is a unique 15-digit serial number assigned to phones and other mobile devices. The IMEI number is printed under the battery or on the back of a phone or other device, and it is different for each device.
The IMEI number is used to identify a particular piece of mobile equipment. It is used in the event that a phone is stolen, and it can also be used to obtain the specifics on the operating system of a phone. Many phones also have a special feature that allows users to see the IMEI number of the phone without having to remove the backing or the battery. Depending on the brand of phone, the sequence *#06# can be typed into the keypad of the phone, and the IMEI number will be displayed on the screen of the phone.
Certain carriers have the ability to block or lock the IMEI number that is associated with a specific phone. Carriers may do this because the phone has been stolen or lost, or a bill has not been paid for the phone. When an IMEI is blocked on a phone, the phone is generally useless to a certain carrier and will often become inoperative.