To unlock a SIM card that is locked by a PUK code, log into your wireless account on your carrier's site. Major carriers, such as AT&T and Verizon, provide the device's PUK code in the device information section of the account.
If the PUK code is not available online or the displayed code does not work, contact your carrier's customer service department. AT&T states that customers whose devices ask for PUK2 codes must contact customer service for assistance. These PUK2 codes are not available in the online account information.
PUK codes automatically lock SIM cards when a device's passcode is entered incorrectly too many times. Users can also choose to lock the SIM with a PUK code. An unobtainable PUK code cannot be removed; the only way to unlock the device without this code is to insert a new SIM card. SIM cards locked by a PUK permanently deactivate once 10 incorrect codes are entered. A new SIM card must be inserted to make the device usable again.
PUK codes are only applicable to GSM phones, including all AT&T and T-Mobile phones. Sprint and Verizon phones that use LTE are also GSM phones. Older Sprint and Verizon phones that utilize CDMA technology cannot be PUK locked. This is because these devices do not use SIM cards.