PIN stands for Personal Identification Number. When you switch off your mobile and switch on again it will ask your PIN No. If you enter the PIN No three times wrong then your mobile will ask for the PUK
The PIN and PUK are provided on your SIM package, and can be changed many times. The basic purpose of these codes is to provide a security
.These codes are normally used to prevent your SIM card from unauthorized use.
code from the package that has come with your SIM card Get these codes from SIM package and unlock your mobile phoe.But if you have changed your PIN and now have forgotten it then there is also a way to resolve it. When you give an incorrect PIN three times to your mobile phone it will block your SIM card, then in this case you have to provide a PUK given to you by network provider. And you can get your PUK any time by calling at the help line number of your network service centre