Apple’s iPhone 4S will still have network limitations, even when you pay extra to buy the unlocked version.

The company revealed today that it will offer an unlocked version of the iPhone 4S — meaning it’s not tied to a specific carrier — for $649 starting in November. But the unlocked iPhone 4S will only work on GSM networks, such as AT&T’s in the U.S., even though the phone also has the ability to work on CDMA networks (like Verizon and Sprint).

Apple began accepting pre-orders for the iPhone 4S early Friday morning. When it was announced on Tuesday, Apple described the 4S as a “world phone”, since it works across both major 3G cellular standards. Now that description seems a bit false, since even an unlocked iPhone 4S isn’t free to work across all networks.

Still, for plenty of users the unlocked iPhone 4S will be immensely useful. It will allow them to travel across the world and swap out their SIM card so that they’re only paying local rates for voice and data service. It was likely too difficult for Apple to open up the iPhone 4S to all CDMA networks, since those networks typically don’t rely on easily removable SIM cards.

In addition to the $649 16 gigabyte unlocked iPhone 4S, Apple is also offering 32GB and 64GB versions for $749 and $849, respectively.