Too Little, Too Late
The Pre looks to me to be a pretty well-designed and thought out smartphone, though I have yet to touch and play with one. That said, I think it's still destined for failure for the following reasons:
1) Sprint - they have enough issues of their own to cause problems and limit the sales and the appeal of the Pre. (And just how many people currently pay enough per month for their iPhone plan that they'd actually save the $1,200.00 figure touted by Sprint? I know that I certainly wouldn't).
2) Palm is just too late to the game. They generally started the smartphone market, but just as with their original PDAs, they didn't stay in the forefront and got passed rapidly by the other players. Because of this, many of the folks developing applications for their platforms have evaporated and Palm will have a difficult time getting them back. Without all the little apps that make the phone fun, truly useful, and totally customized the way each user wants it to be, Palm won't be able to generate enough momentum to sustain the Pre and make it a successful product.
It's really quite a shame, actually. Choice and new ideas are generally very good things.
Finally, as far as the iPhone not working fully with T-Mobile's 3G network, this is no big deal. With a bit of code tweaking for the transceivers in the iPhone, it could be up and fully functional on that network too. That's how they make it work on the rest of the world's networks. There's only two base requirements: first, it must be a GSM network; and second, it must operate in the four frequency bands covered by the iPhone, which pretty much covers them all.