Despite its superficial similarity to the iPhone 4, three landmark features set the iPhone 4S apart from its predecessor: Siri, the new 8 megapixel camera, and the much more powerful A5 processor. The iPhone 4S also comes with a few more subtle design tweaks that differentiate it from the iPhone 4, and you might miss some of those changes if you didn't have an iPhone 4 and 4S sitting side-by-side for a comparison.
Antenna Improvements
Phil Schiller actually did talk about the new antenna in the iPhone 4S during the most recent Apple event
