Apple is now selling unlocked iPhone 4 handsets in North America. The handsets are available to purchase for $649 (16 gigabyte) and $749 (32 gigabyte) respectively.
As outlined by Apple in the handsets’ description:
Get all the features of iPhone 4 — FaceTime video calling, Retina display, HD video recording, and more — in a phone that you can activate and use on the supported GSM wireless carrier of your choice, such as AT&T in the United States.1
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.