Well i dont see any drastic changes in the iPhone 4S except having 8 megapixel camera, World Phone(GSM or CDMA) and A5 processor. iOS 5 which will be launched soon which is now available on the new iPhone 4S can be any ways put on iPhone 4 and some other Apple devices leveraging all the features there are. So i think one should wait for the iPhone 5 as it is rumored to be having larger display screen as compared to iPhone 4S, wouldn’t it be nice to see the top and the bottom spaces occupied. It will be nice to see a iPhone much wider and better resolution rather than the same look.
Difference between 4S and 4: http://www.apple.com/iphone/compare-iphones/