It’s confusing, because it means two different things.
1. As far as the iPhones are concerned it is just a model #. There is an iPhone 3G, 3Gs, 4, and 4s. Not to mention the 3 iPhone 5 models. So pretty much the only differences betweenall of them are looks and processing power. There are three different looks for the phone 3G, 4 and 5. The when they put the “s” on the end, it means it is their higher end model with beefier guts. Also, the 4s is when they started supporting sirii. The iPhone 5 is when they started supporting 4G. See #2
2. 3G and 4G refer to mobile data network speeds. It actually doesn’t effect us much up here because the only places 4G is available is downtown NC and downtown GV. 3G is almost always sufficient for most people. 4G is a lot faster, but in my opinion more of a marketing gimmick.