Hi if you want to unlock your Nokia mobile from globe network provider to freely use it with AT&T sim then code is the best solution to unlock it .You can purchase code from online providers like OnlineGSMUnlock.com for affordable cost .You first check that whether the code is available for your mobile model ,country and network provider .If yes then pay for it and unlock your phone ...

If it is the SIM card that is blocked you need the PUK code! This is available from your service provider!