Check if Your iPhone is Unlocked

If you purchased your iPhone from a carrier such as AT&T or Verizon chances are that the phone is locked. Typically locked phones are restricted to operating only on that network.  Phones that were purchased locked are typically subsidized by the network carrier making it far cheaper than an unlocked phone that has no subsidies. Unlocked phones allow you to switch the phone to any network carrier you choose without penalty.  You can do that by simply changing the SIM chip in your phone.