What does Unlocking an iPhone do exactly?
Unlocking an iPhone would give you access to use any GSM network SIM card with it. But certain unsafe unlocking methods may give reduced performance on iPhone. One of the safest and easiest method to unlock an iPhone is to unlock using remote unlocking service. You can get the remote unlocking service for an iPhone from www.theunlockarena.com at affordable coct with easy unlocking instructions. Good luck mate.
The apple iPhone is a carrier specific device which means traditionally iPhone users had to sign up with a 2 year contract with AT&T (or other official wireless carrier in contract with Apple) in order to enjoy all the iPhone functions. Unlocking an iPhone simply allows for a cross carrier operation via a simple SIM card swap.