If you have forgotten your mobile access PIN and enter it incorrectly three times, you will be asked to enter the phone's PUK code.
The PUK code is an 8 digit number that you were given when you first purchased your SIM card. The PUK code is printed on the SIM packaging. If you sign up for My Sure you can find your PUK code at any time.
Click here for more information on My Sure.
Click here for instructions on how to find your PUK code in My Sure.