A GSM phone will ask for a PUK code when the user has entered the wrong PIN unlock code too many times. PUK is short for “PIN unlock key.” When the phone asks for a PUK code, the SIM card is locked and the phone can no longer make or receive calls. Users must get the PUK code from their wireless carrier. AT&T Wireless allows users to retrieve the PUK code online, but T-Mobile users must call customer care. Tips
