What is an IMEI ?
The IMEI (i.e. International Mobile Equipment Identity) number is used by a GSM network to identify devices attempting to connect to them and therefore can be used for stopping a stolen phone from accessing that network. It's only used for identifying the device and has no permanent or semi-permanent relation to the subscriber. The IMEI number includes information on the origin, model, and serial number of the device.
IMEI = 14 digits + 1 Check Digit
IMEISV = 14 digits + 2 Digit Software Version Number
IMEI + SV = 14 digits + 1 Check Digit + 2 Digit Software Version Number
The format of the IMEI is AA-BBBBBB-CCCCCC-D, (15 Digits) although it may not always be displayed this way. The IMEISV drops the Luhn CD (i.e. Check Digit) in favour of an additional two digits for the SVN (i.e. Software Version Number), making the format AA-BBBBBB-CCCCCC-EE. The IMEI+SV incorporates both the check digit and the additional two digits for the Software Verison Number, making the format AA-BBBBBB-CCCCCC-D-EE.