This expert is helping you out because there weren't many active AT&T Wireless experts.
"A PUK (PIN Unlock Key) code is required to unlock SIM cards that have become locked following three successive incorrect PIN entries. If your SIM card becomes locked, you will need to get a PUK code from AT&T to unlock your SIM card.
You can obtain your phone's PUK code from AT&T in one of these ways:
Log in to your myAT&T online account
Use our Technical Support Chat
Contact Customer Care at 800.331.0500
Find the PUK Code for your phone online
Go to the My Phone/Device page in myAT&T.
From the My Phone/Device screen, select the Unblock SIM Card link under Manage my phone/device.
The Unblock SIM screen will display your PUK code and will give you instructions for unblocking your SIM Card.
Once you receive your PUK code, you will need to enter it into your phone to set a new PIN code.
I would like to say thank you for coming to us for help. I hope you found my answer useful and if so would you please hit the green smiley face and then click the "accept this answer" under our discussion or "don't want any more answers" under our names if you are satisfied with my response as well please to close the question. This is how we are rated and we all work really hard to provide the best answer possible. Its been a honor assisting you today and look forward to helping you again in the future. Thank you again for using our service.
THank you so much geek. I will follow the link you provided.