IMEI (International Mobile Equipment Identity) is 15 digit or 17 digit (IMEISV) unique number for GSM and WCDMA mobile phones, used to identify the device.
- Usually IMEI is printed in a label under the battery compartment with many other technical details, and this is hard-printed IMEI.
- To read IMEI on screen type *#06#. Onscreen keypad phones first bring the keypad onscreen and type code *#06# phone will display IMEI on screen, this is soft-coded IMEI
The second method is preferred to get IMEI for code calculation, because usually phone uses programed IMEI to check the entered unlock code.
Read more information http://en.wikipedia.org/wiki/International_Mobile_Equipment_Identity