"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple Begins Offering Unlocked iPhone 4S in U.S. Online Store
Pricing for the unlocked, contract-free iPhone 4S comes in at $649/$749/$849 for the 16/32/64 GB models respectively. The unlocked device is compatible only with supported GSM networks, and Apple offers some advice on which customers might benefit most by purchasing an unlocked iPhone.
The unlocked iPhone includes all the features of iPhone but without a contract commitment. You can activate and use it on the supported GSM wireless network of your choice, such as AT&T in the United States.* The unlocked iPhone 4 or iPhone 4S will not work with CDMA-based carriers such as Verizon Wireless or Sprint.Apple had previously announced as pre-orders went live in the United States back in early October that unlocked models would become available in November. The company's retail stores, however, began selling off-contract phones immediately after launch, with customers discovering that those devices were also coming through unlocked.
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 arrives without a micro-SIM card, so you’ll need an active micro-SIM card from any supported GSM carrier worldwide. To start using it, simply insert the micro-SIM 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.