As promised, here are some nokia codes, use them at your own risk, i take absolutely no responsabilty if your phone gets screwed up...
How to reformat Nokia series 60 (7650/6600/...) phones ?
First off, make sure you have full battery since formatting can take some time and if your batteries die in the middle of the process then you'll screw up the phone. Then type this code: *#7370# on main phone screen. This will completely format your device and will reboot, your mobile would be as "new" as straight from the box aftwerwards... Do not touch anything during the process! I recommend you even connect your phone to the charger just to be on the safe side.