There are set of default codes built into most Nokia devices. Many people are unaware of these and it is rarely published in any official Nokia documentation. These can be handy at times, so here goes:

IMEI number (International Mobile Equipment Identity):

*#06#

This number is a unique ID number for you handset and is often required for insurance documents or for reporting stolen handsets to the police. It’s handy to kee a record of this. It can also be found on the phone under the battery and is also printed on the fancy bar-code on the box of the device.\

Firmware Version:

*#0000#

This is particularly necessary when installing certain apps or when trying to figure out if you have the firmware installed on your phone. Be sure to look out for the latest firmware update that everyone is excited about for the Nokia N97 in a few weeks time!

Software Format phone:

*#7370# (or *#res0#)

This will delete all the data on your phone and restore the memory to the state it was during shipping. It is usually followed with a “Are you sure?” prompt, but there definitely isn’t a “Are you sure that you are sure?” prompt, so be careful with this one!

Handset Settings Reset:

*#7780# (or *#rst0#)

This code resets the device settings back to default shipping values. All your data will remain on the device, however all settings will be changed back to default.

Total Power On Time:

*#92702689# (or *#war0anty#)

This should give you a total time that your device has been on. It’s a good thing to check when purchasing a second-hand phone.

These are all that I am aware of, but if you know anymore, please mention them in the comments and I will be sure to update the post.