Here are a bundle of # codes for nokia phones. Quite a few of them work for my N70 and my 7610 so i imagine they work on a lot of phones - but use at your own risk.

*#0000# Check firmware version*3370# This Nokia code activates Enhanced Full Rate Codec (EFR) - Your Nokia cell phone uses the best sound quality but talk time is reduced my approx. 5%

#3370#*#4720#*#4720#*#0000#*#9999#*#06##pw+1234567890+1##pw+1234567890+2##pw+1234567890+3##pw+1234567890+4#*#147#*#1471#*#21#*#2640#*#30#*#43#*#61#*#62#*#67#*#67705646#*#73#*#7370#*#746025625#*#7760#*#7780#*#8110#*#92702689#*#94870345123456789#**21*number#**61*number#**67*number#

12345 This is the default security code

Press and hold # Lets you switch between lines