The iPhone 4s has an upgraded "4g" radio that gets 4g like speeds on at&t's network. I've pasted a speed test below and I was able to get over 9mbps download and 1mbps upload in the Cincinnati area. I've pasted a screenshot.
This may not be true 4g but it is a definite upgrade over the 3G in the iPhone 4. Something to consider depending on the quality of at&t's network in your area.