The International Mobile Equipment Identity or IMEI (pronounced /aɪˈmiː/) is a number unique to every GSM and WCDMA and iDEN mobile phone, as well as some satellite phones. It is usually found printed inside the battery compartment of 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. 

Action:
On the main screen type *#06#

Result:
 IMEI can be displayed on the screen.

Information you get from the IMEI (International Mobile Equipment Identity)

XXXXXX	XX	XXXXXX	X
TAC	FAC	SNR	SP

                                      

TAC - Type approval code of your nokia Mobile
FAC - Final assembly code of your cellphone
SNR - Serial number of your nokia Phone
SP - Spare