It works using Gevey Sim given that iPhone 4 is for AT&T. Verizon model won't work. Unlocking is not mandatory. U can unlock using the Gevey Sim if the phone is jailbroken. You can buy Gevey Sim for $5 on ebay. Just make sure the phone is jailbroken or jailbreakable. iOS 5 is not jailbreakable.