Find the pin unlock key, or PUK code, for your SIM card at AT&T’s online portal myAT&T. The company’s website has the link to log in to myAT&T on its homepage.
Use your 10-digit number or your AT&T AccessID to log into myAT&T. After logging in, select Wireless from the menu at the top of the page. Next, click on Phone/Device tab and then choose the Unblock SIM Card option. This opens another page which contains the eight-digit PUK code for your SIM card.
To unlock your SIM card with this PUK code, enter the PUK code into your phone and press OK. Then select a new PIN code and press OK. When prompted, re-enter this new PIN code into your phone. Enter the PUK and PIN codes correctly to unlock your SIM card.
Setting a PIN code to access your SIM card protects the SIM card from unauthorized use. However, entering an incorrect PIN code more than three times blocks the SIM card. The phone then displays a prompt for a PUK code. Entering the PUK code incorrectly more than 10 times results in the phone displaying a PUK2 error. A PUK2 error means that the SIM card is permanently locked.