If you enter the wrong PIN more times than the maximum number of attempts allowed, your SIM card will become “PUK-locked.”
You need a PUK code to restore access to HTC Sensation. This code may have been provided by your mobile operator when you received your SIM card.
On the Phone dialer screen, enter the PUK code, and then tap Next.
Enter the new PIN you want to use, and then tap Next.
Enter the new PIN again, and then tap OK.