A couple of months after iPhone 5 went on sale, Apple started selling the factory-unlocked GSM iPhone 5 models in the United States on its Online Store from Thursday night.

The unlocked GSM iPhone 5 is available for $649, $749 and $849 for the 16, 32 and 64 GB models respectively. Apple also has declared an estimated shipping time of one week. The unlocked models will work on both AT&T and T-Mobile.

From Apple’s official site:

“The unlocked iPhone includes all the features of iPhone but without a wireless contract commitment. You can activate and use iPhone on the supported GSM wireless network of your choice, such as AT&T in the United States. The unlocked iPhone 4, iPhone 4S and iPhone 5 will not work with CDMA-based carriers such as Verizon Wireless or Sprint.

If you don’t want a multiyear service contract, or if you prefer to use a local carrier when traveling abroad, the unlocked iPhone is the best choice. It does not come with a micro-SIM card for iPhone 4 and iPhone 4S, or a nano-SIM card for iPhone 5, so you’ll need to get one from any supported GSM carrier worldwide. To start using it, simply insert the card into the slot on your iPhone and turn it on by pressing and holding the On/Off button for a few seconds. Then follow the onscreen instructions to set up your iPhone.”

Apple has already offered an unlocked version of iPhone 5 in other countries around the world, including Canada and Europe, after the device was launched in September. But as it had done before with the unlocked iPhone 4S last year, the company delayed the launch of the unlocked iPhone 5 in the U.S.

In case of iPhone 4S, it took only less than a month for Apple to begin selling the unlocked versions of the device in the U.S.

9To5Mac reported, citing “several retail sources,” that Apple would soon sell the unlocked iPhone 5 models in its chain of retail stores, perhaps as soon as Friday.

“The devices have begun arriving in large quantities over the past couple of days to Apple stores,” the report added.

Reports also said that Apple would expand its Personal Pickup program for iPhone 5 that would allow the customers to reserve a device at any time, not just after 10 p.m., for pickup the next day.

Click here to check if your iPhone is factory-unlocked.