Iain Mac
its because you have been playing with it and have fucked it up
tell the truth
http://www.o2.co.uk/apps/getPUK/welcome
3 it seems
If you suspect that your handset has become blocked, you may need a PUK Code. PUK stands for Personal Unblocking Key. If you have entered your PIN code incorrectly 3 times your sim card will be blocked and you will be unable to make and receive calls/texts.