here are the instructions on how to unlock your phone.

1 - Switch on your Nokia N900 without any sim card.
2 - Don't bother as to what is displayed on your Nokia N900.
3 - Compose #pw+CODE+7#.
4 - The Nokia N900 would then display the message "SIM Restriction Off" and will be unlocked!

The letter p appears if you press the button star(*) three times quickly
The letter w appears if you press the button star(*) four times quickly
The symbol + appears if you press the button star(*) two times quickly
The CODE you need to enter is the unique unlock code for your Nokia N900

if you have any doubts in these instructions you can get the instrutions from this site http://www.mobileunlockguide.com/nokia-n900