NEW YORK — Apple Inc. on Tuesday started selling "unlocked" iPhones in the U.S. for the first time, allowing owners to switch carriers to a limited extent and save money when travelling.

Apple is selling them on its websites and its store for $649 and $749 depending on how much memory they have. They're identical to the versions sold for use on AT&T Inc.'s network, but don't require a two-year contract.

The buyer will separately have to buy a Subscriber Identity Module, or SIM card, from a carrier to activate the phone. Apart from AT&T, the only national U.S. carrier that's compatible with the phone is T-Mobile USA, and it can provide only phone calls and low data speeds. Its U.S. "3G" wireless high-speed data network isn't compatible with the iPhone.

Many overseas carriers, however, are fully compatible with the phone, so international travelers can switch out their U.S. SIM card with one from the local country to avoid AT&T's international roaming fees.

Apple already sells unlocked iPhones in all other countries where the phone is available, according to Apple spokeswoman Natalie Harris.

Hackers have also made a sport of unlocking iPhones, freeing them up for resale and use in other countries.

AT&T sells iPhone 4s that are locked but don't come with contracts, also for $649 and $749. Spokesman Mark Siegel said AT&T will not sell the new unlocked phones.

AT&T does not let customers unlock older iPhones either. The company provides unlock codes to customers with other phones if their contracts have expired or they're willing to pay an early termination fee.

Unlocked and no-contract phones are more expensive than phones sold under contract because carriers like AT&T subsidize phones that come with contracts, figuring that they will make their money back through service fees.

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