If you don't have the code and try to unlock it too many times incorrectly, it will ask for PUK code. PUK code can be received by calling into customer care(18003310500) or heading into a corporate AT&T store. If its actually saying "PUK Blocked" then you'll need a new SIM card which is still free if you head to a corporate AT&T store. I hope this helps!!
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13 Years in the industry
I've worked in the cellular industry for 13 years. I'm big on fixing the phone yourself when ever possible before having to call some annoying 800 number. So I will always try and give you all the self diagnosis answers I have to be able to fix it first.
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I have worked for a Sprint/Nextel advanced wireless center, Directv, ATT UVERSE and ATT wireless; also managed a 128 square mile wireless network that provided high speed wireless broadband. I earned a Summa Cum Laude Bachelor's Degree and served as a Air Traffic Control communications electronics technician in the USMC. I also served in the US Navy as a satellite communications technician. Over 20 years of experience in computers, networking and wireless. Technology GeeK extraordinaire. I am able to fix just about anything that has electrons flowing through it. Customer service and satisfaction is very important to me. Number one rule is treat everyone like you would want to be treated. Try Me :-)
SIM cards are locked after three incorrect PIN entries in a row. To unlock your device's SIM card, you'll need its PUK code. You can get the PUK code online by following these steps:
Select myAT&T at the top of the page. If prompted, log in. Don't have a myAT&T login? Register today.
At the top of the page, hover over Wireless Services, and then select My Phone / Device.
If necessary, click Select and choose the mobile number that needs the PUK code.
Under Manage my phone/device, select the Unlock SIM card using PIN Unlock link.
On the Unlock SIM Card Using PIN Unlock Key screen, view your PUK code and follow the instructions for unlocking your SIM Card.
You can also log in and chat with us online or call us at 800.331.0500 or 611 from your AT&T wireless phone for help unlocking your SIM card.
PUK blocked call operator or PUK2 error messages
If your device displays PUK blocked call operator or PUK2, your SIM is permanently locked because the wrong PUK code was entered 10 times in a row. You'll need to get a new SIM from an AT&T Retail Store or by calling us at 800.331.0500 or 611 from your AT&T wireless phone.