Nokia Secrets (may works on all models)

Check the IMEI*#06#
Check software version
*#8110#
Sim Clock Stop
*#746025625#
Warranty menu
*#92702689#
Press the following warranty code
6232 (OK) Displays the Month and Year of Manufacture
7332 (OK) Displays the date of the last repairment
7832 (OK) Displays the date where the phone was purchased
9268 (OK) Displays Serial Number
37832 (OK) Set the Purchasing Date MMYY
87267 (OK) Transfers ALL phone numbers, pictures, sounds from one phone to another
Hands Free
To continue an existing call when placing the 8110i into the hands free car kit without it dropping the call, press the Memory button just before connecting the cable and placing it in the cradle.
Display extra text in call costs feature
If your network operator doesn’t offer a call costs service, you can still make use of that function to display some personalized text on the screen of your 8110i. Go to Menu, [5], [7], [1], enter PIN2-code and choose Set. Then type in the limit of the currency units you’re using (if the call cost service worked, you would have to type the cost limit of the calls) and choose OK. In this case I typed 8110. Then go to the next sub menu (Menu, [5], [7], [2]), the Show costs in menu. Type in the PIN2 code again and select Currency. Type in the unit price, in this case number 1. Then type the name of the currency – you can use any string of letters and numbers 1-3 characters long. then type 2 letter then to confirm type two names beginning with one of each of the letters. Then press OK to confirm it.
Quick saving while in call
Saving numbers to memory during a call If you type a number into your phone during a call, you will lose it when the call ends. To prevent this happening just hold down Memory button — the number will be saved (with no name) to the next available memory location.
Deleting SMS messages quickly
When reading an SMS message, instead of pressing Option, Erase to delete the message, simply press [C].
Turning lights on temporarily
If you have display lights turned off, you can turn them on by quickly pressing and releasing the power button. They will stay on as long as you are pressing button.
Silent mode temporarily
You can put your phone into silent ringing mode temporarily by pressing Menu then [#].
Closing the cover without ending a call
If you press the menu key and then close the sliding cover during a call you will not end your call.