These directions are for an AT and T phone, but other than that would be the same for any carrier.
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 your phone carrier to unlock your SIM card.
You can obtain your phone's PUK code from your carrier in one of these ways:
Log in to Your account.online
Use a Technical Support Chat
Contact your carriers Customer Care
Get Your Phone's PUK Code Online
Go to the Phone/Device page.
From the My Phone/Device screen, select the Unblock SIM Card link under the My Make & Model heading.
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.
Note: If you enter the wrong PUK code 10 times in a row, your SIM card will be invalidated, and you will need to purchase a new SIM Card. The phone will display the following error: "PUK blocked call operator
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