Few people use PIN locking systems to lock their phones to avoid unauthorized access. Though this is a good option, it pisses you off sometimes. Three wrong entries of the PIN code will result in SIM blocking. Once SIM gets blocked, the phone starts asking PUK code to enter. If you again enter the wrong code three times, SIM gets completely blocked. You have to walk into your service provider outlet to get a replacement SIM card.
How to find PUK code on the 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 an easier way of getting a PUK code. For getting the PUK code of an 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 work or your service provider is not Airtel, call customer care using any other mobile phone which uses the same service provider. They will ask for 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 for 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.