I predict it'll be like every single other gaming/phone hybrid, and completely flop with regards to penetrating the general gaming audience. I think it will do a good job of giving those who already have an iPhone something extra to do, but won't convince many people to buy it with gaming in mind.
The phone itself isn't really too great with regards to value for money, so it's not really going to convince anyone who wasn't already prepared to (over)pay for it to do so. People could buy a Nokia phone or something that far surpasses the iPhone and a DS Lite or PSP, and still pay a comparable price to one iPhone.
It sounds OK on paper, but then so did the NGage to a lot of people, and the 'mobile phone gaming revolution' has been "just around the corner" for years upon years now. My gut feeling is that people won't bite.