PIN is the personal identification number, a guarded number that is given to you by the phone service provider when you get a new number for your phone. Most phone service providers usually lock the phone and you need to use this PIN which specific to the phone number and not the instrument you use- which means, you can use the PIN to unlock any phone provided you use the same, relevant phone number in whatever instruments). Unlocking means gaining access to the device you are using. You need to press the 4-digit number to unlock the device and it starts functioning.