pour retrouver tout seul son code déblocage / désimlockage:

http://www.peters1.dk/unlock/nokia/online.php?sprog=fr

Attention, au bout de 3 essais infructueux, le portable est bloqué (meme avec le bon code), il faut le réinitialiser. (le brancher sur un pc avec un logiciel nokia), voir ici :

http://forum.lesmobiles.com/orange-desimlockage/impossible-d-annuler-la-restriction-t86117.html

sinon, faire un hard reset...

http://www.hard-reset.com/nokia-3510i-hard-reset.html

Nokia 3510i hard reset

Restore factory settings
To reset some of the menu settings to their original values, press Menu, select Settings and Restore factory settings. Key in the security code and press OK. For example, the names and phone numbers saved in the phone book are not deleted.

You can format your Nokia 3510i device by typing: * + 3 + call + Power on. Before the device is reset, you need to provide the lock code. The default lock code is 12345.
If it is not working try this code:
You can format your device by typing *#7370# in standby mode. Before the device is reset, you need to provide the lock code. The default lock code is 12345.