Nokia Secret Codes
These codes for the Nokia series of phones unlock some hidden functions.Use the codes at your own risk, not all Nokia phones support all codes.
How To Find Out What Firmware Version You Have
You can find your phones firmware version by entering *#0000# on the phone while it is in standby.
Restore Factory Settings
Enter *#7780# on the phone while it is in standby.This will reset it to the factory settings and wipe most of the stuff from the phone (contacts, connection settings etc).
Display handset’s IMEI (International Mobile Equipment Identity) Number
Enter *#06# on the phone while it is in standby.
Display Handset’s Warranty
Here you can view the S/N and the IMEI as well as the life timer (newer models). The date the phone left the factory and the date it was purchased. If your phone has been repaired the date of the repair is also visible. You will need to turn the phone off to exit this menu. Newer phones simply require you to press ok.
Display the Bluetooth MAC address
*#2820# (Phone must have a built in bluetooth adapter)
Reset the mobile wallet
*#7370925538# (Phone must have the mobile wallet feature)
More codes to be added soon…
Source : Netlife and Nokia Discussion Forums