format the nokia 6600

*#7370#

make sure the battery is full or your phone is on AC

have your lock code at hand (default is 12345)

all contacts, messages, settings and user-installed applications will be gone after the operation completes.

There is a thread for this: http://www.allaboutsymbian.com/forum/showthread.php?s=&threadid=17507

Hope this helps 😊