If you are locked out of your phone, it may ask you to enter the PUK code in order to unlock it.
All SIM cards are protected with a PIN number. The PIN (Personal Identification Number) is provided to you when you purchase the sim card. Standard PIN codes are 4 digits in length. If you forget your PIN, or enter the pin incorrectly 3 times, then the second security measure known as the PUK code is enabled. The PIN and PUK codes can be found on the SIM card packet that is provided to you when the sim was purchased. There is a PUK 1 and PUK 2 code to help with securing your SIM pin. You can use it to unlock a blocked SIM pin.
How to access SIM PIN & PUK
Turn to the back of your sim card holder. Your PIN & PUK will be displayed as shown below.
It is important to keep your SIM card holder in a safe place.