Apple has begun selling factory unlocked iPhone 4 GSM model in the United states. An unlock iPhone can be used on any supported carrier and offers all the features without a commitment.
If you don’t want a multiyear service contract or if you prefer to use a local carrier when traveling abroad, the unlocked iPhone 4 is the best choice. It arrives without a micro-SIM card, so you’ll need an active micro-SIM card from any supported GSM carrier worldwide.
The 16GB iPhone 4 black model starts at $649 and the 32GB variant costs $749. Factory unlocked iPhone 4 are available in both black and white.
Apple explains how the unlocked iPhone 4 works:
The unlocked iPhone 4 requires an active micro-SIM card that you obtain from a supported GSM wireless carrier. Simply insert the micro-SIM card into the slot on your iPhone, connect to your Mac or PC using the USB cable, and launch iTunes on your computer to complete the setup.