Apple isn't stupid; the iPhone will be available from all carriers at some point in the future. Most "fancy" phones, like the Razr, are limited to one carrier at first, before they become widely available. (Remember when all phones were carrier exclusive?
I really, really, really want an iPhone, but a) Nothing could make me switch from using Verizon, and b) Nothing could induce me to buy a 1st generation Apple product. By the time the iPhone is no longer AT&T exclusive, many of the bugs will be worked out, and the price will have dropped. I also theorize that battery kinks will have been worked out, and the hard-drive space will have increased-it's pretty paltry compared to an iPod.
I like it because I DO carry my iPod and and phone around with me everywhere, and it's annoying. I'd much rather have the one device.