Apple has announced that an unlocked version of the iPhone 4S will become available in November. The company neglected to touch on the subject earlier this week during the 4S unveiling.

The unlocked iPhone 4S is only being made available in the US through AT&T. Since AT&T is a GSM network, your unlocked device will only work on other GSM networks. This excludes Verizon Wireless and Sprint in the states, which are CDMA-based carriers.

The benefits of an unlocked phone include being able to travel abroad and use a micro-SIM card from a local carrier rather than racking up expensive out-of-country fees. Additionally, unlocked phones are sold without a contract so you are free to discontinue service whenever you want without paying a hefty early termination fee.

An unlocked phone doesn't come cheap since there are no carrier subsidies to offset the hardware cost. The 16GB model is $649, a 32GB unit costs $749 and a 64GB iPhone 4S will set you back $849. Meanwhile, the unlocked iPhone 4 has been displaced to a lower price point and it now costs $549 for the sole 8GB model – also on AT&T.

CNET has learned that Apple has started taking pre-orders for unlocked models in other countries. For example, the UK 16GB, 32GB and 64GB models retail for 499, 599 and 699 pounds, respectively.

Carrier-specific iPhone 4S' are available for pre-order in the US starting today through Apple and wireless providers AT&T, Sprint and Verizon. The phone is available in 16GB, 32GB and 64GB capacities for $199, $299 and $399 (with a two year service agreement) respectively in white and black. Phones will become available starting October 14.