A pin is a secret numeric password shared between a user and a system that can be used to authenticate the user to the system. If you have not changed the original PIN of your SIM then you can get easily this code from the package that has come with your SIM card. Get these codes from SIM package and unlock your phone. 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.