Rather shortsighted, don't you think? You've signed a two year contract for a two-year-old piece of hardware (the CPU/RAM are the same in the 3G as they were in the original iPhone) ... The 3GS is literally twice as fast with twice as much RAM. You don't think that soon - within the next 6-12 months, probably; 12-18 months definitely! - there aren't going to be apps that will require the newer hardware? You don't think that developers are going to start taking advantage of the added horsepower very soon? I think buying a two-year-old computer is pretty silly, especially when the newer model is literally twice as fast with twice as much RAM and twice the storage as the older model and costs the same or less.I bought a 3G last week with plans to try it out and return it to get a 3GS but I've decided to keep the 3G. I probably won't even notice it's 2 times faster and my ipod touch and 3G already seem fast enough for me. I'd never use voice control, I can just drop a pin in maps to see if I'm going in the right direction, and I jailbroke my iphone so I can record video which I probably won't do anyway. 3G is fine for me!
Your call, of course. But if you decide to keep the 3G, I can all but guarantee you'll regret that choice, and probably sooner than you think.