There are certain models of Nokia that cannot be unlocked by a simple code
. The phone will display the message "Cannot undo restrictions", which basically means that the phone is hard locked and there is no means to unlock it with a code. If this is the case, you can use professional phone unlocking services that you can find online or go to your nearest local cell phone technician for help. You can try to search the web for reputable company that offers phone unlocking services.