How To Reset / Format Nokia Symbian Phones
1. *#7780# –Soft reset
2.*#7370# – Hard reset
3. Hard reset – hold the following buttons * (star key), 3 (number button) and talk/green key for s60v3 based devices. Turn on the phone and do not release those buttons until you see the Nokia boot up screen. Once you feel the phone power up you can let go off only the power button while still holding all three buttons.
For Nokia N97 Backspace/SpaceBar / Backspace while holding the power button. Again do not let go until you see the handshake screen.
For Nokia 5800XM – use the following buttons to do a hard reset, /Green/Red/Camera keys pressed all at once on power up.