How do I unlock my Galaxy S3?

Solution
If you enter it wrong several times, it should prompt you for the Google account you used to set up the phone. Enter that.

It's also possible you set a SIM PIN. If so, it'll ask you for a PIN Unblock Key (PUK) - this should have come with your SIM card, or you can get it from your cellphone company.
If you enter it wrong several times, it should prompt you for the Google account you used to set up the phone. Enter that.

It's also possible you set a SIM PIN. If so, it'll ask you for a PIN Unblock Key (PUK) - this should have come with your SIM card, or you can get it from your cellphone company.
 
Solution