.Hi! If your prepaid sim card was originally bought with a gophone device, chances are ur prepaid sim is locked to the device or not. To determine if it's locked, insert your prepaid sim to the iphone. When you turn it on & you can get through, then of course u can use the iphone. If you get an error such as sim lock, you have to insert your prepaid sim to the original device you purchased it with and call 611 to have it unlocked. Just make sure you can still turn the device on.