Most of the time when you join a network you get a cell phone at a discounted price for signing or renewing a contract. However, these phones, including iPhones, are typically in a locked mode so that they cannot be used on other carrier’s networks. There are some ways to unlock an iPhone but first you probably need to know how to tell if your iPhone is unlocked or not.
To check about the state of the iPhone simply open the SIM card holder on the iPhone. This can be done by using something like a stick pen or a straightened safety pin to press in the small hole which will release the tray. Once the tray is opened remove the SIM card from the iPhone. Now put in a replacement SIM card that you know is working on another network provider. Turn the iPhone on and try to place a call. If you can place a call successfully the iPhone is unlocked. If you cannot place or receive a call then the iPhone is locked.
Unlocking an iPhone is a relatively simple process that will allow you to use the phone on different networks as long as you have the SIM card.