Just to chime in here, I have a Samsung Blackjack which is 3G (AT&T) and also an IPhone which is Edge. Without a doubt the 3G is way faster. I've never traded through my phone, but would think with the Blackjack it would be no problem - as fast as it is. I really like the Blackjack it is a nice phone, however, the IPhone is just better, more intuituve, cooler, on and on .... If they actually release the IPhone with 3G, it will be as close to the perfect phone you can get, in my opinion.
Also of note, since Apple recently released the IPhone SDK, Microsoft is working on porting their Office utilities to the IPhone, something I am very much looking forward to.