Few people use PIN locking system to lock their phone to avoid un-authorised access. Though this is a good option, it pisses you off sometime. Three wrong entry of PIN code will result in SIM blocking. Once SIM gets blocked, phone starts asking PUK code to enter. If you again enter wrong code for three times, SIM gets completely blocked. You have to walk into your service provider outlet to get a replacement SIM card.
PUK code is a SIM specific code assigned by your service provider. No way you can guess & enter it. So, when it asks for the PUK code, don’t do anything, get the PUK code from your service provider. Airtel has a easier way of getting PUK code. For getting PUK code of a Airtel number, send PUK<space>PhoneNumber to toll free number 121. You can make use of any other Airtel number to send this message since your SIM might have been blocked already.
If the above method doesn’t works or your service provider is not Airtel, call to customer care using any other mobile phone which uses the same service provider. They will ask some details about you to make sure you are the owner of the SIM card. Questions might include your billing address, email ID, numbers you recently called or messaged etc. They might even ask you the number printed on the SIM card, so be prepared with all details before calling them. Once you get the PUK code, enter it into the phone & your phone will return to normal.