At this point wait for the iphone 5. Rumored to be coming in summer 2012. The iphone 4S is a weak upgrade of the iphone4 (I have the 4). Steve Jobs made Apple what it is today. His last project before his death was the iphone5. He was not involved with the 4S. APple had production delays on the 5 and did not want to miss out on quarter 4 2011 shopping so they put a weak 4S phone out there.
If you cannot wait for the 5, don't spend the extra money and just get an iphone4.