Confirming rumors that surfaced over the weekend, Apple has started selling the unlocked version of the iPhone 4 in Apple Retail stores.

Only the GSM model of the iPhone 4 is available for purchase without a carrier contract, while the the CDMA model is still tied to a Verizon contract.

Carrier-independence comes with a price, though: the 16 GB version of the iPhone 4 will set you back $649, while the 32 GB model costs $749.

With this move, Apple caters to U.S. users who often travel internationally and who don’t want to be locked in an AT&T contract, which means they can swap SIM cards and save money on roaming fees. Furthermore, international buyers will definitely want to get the contract-free version, whose price can be significantly higher in other countries (for example, an unlocked 16 GB iPhone 4 costs €629 ($909) in Germany, much pricier than the unlocked version in the U.S.).