A SIM card that has been locked by entering an incorrect PIN three times can be unlocked by entering a PIN unlock key (PUK). The PUK can be found on the information sheet that comes with a SIM card or can be provided by the SIM network carrier.
A SIM card becomes locked if it uses the SIM PIN security feature and the PIN has been entered incorrectly three times. If this happens, a PUK is required to unlock the SIM card and allow it to regain full functionality. The PUK is located on the information sheet that comes with a newly bought SIM card. However, if the information sheet cannot be located, it is possible to receive the PUK by logging on to an online account or calling the SIM network carrier and verifying the account password.
Once the PUK has been received, turn on the mobile device with the SIM card inside. When requested, enter the eight digit PUK and press enter. The device will then prompt the user to enter a new four to eight digit PIN. Type in the new PIN and press enter again. Verify the new PIN by re-typing it when promoted and press enter. The SIM card will now be unlocked and resume normal functionality.