The 3G on EDGE that's coming isn't all that much faster. EVDO will still blow it away.

For emails, texting, IMing and browsing the iPhone competes well over EDGE.

But if you could tether on EDGE with an iPhone vs EVDO I think you'd see a huge difference.

The most important, as Xtgirl mentioned, is AT&T reception. I'm 100% sure it's worse than Sprint/Verizon but it's tolerable.