Apple today began offering unlocked iPhone 4S units for sale on its online store in the United States. As noted on the store, unlocked iPhone 4S units will work only on supported GSM networks, such as AT&T in the U.S., and will also allow for use of a local micro-SIM card when travelling internationally. They will not work with CDMA carriers such as Verizon or Sprint. Pricing for the unlocked handset starts at $649 for 16GB units, raising to $749 for 32GB models and $849 for 64GB units. All three are listed as shipping in 1-2 weeks.