I had a hunch that the multi-touch UI would make it into other devices offered by Apple. Using iphone.domain.com or domain.com/iphone seemed shortsighted to me.
In the long term, I think the most important thing about the iPhone/iPod is that they raise the bar for mobile devices. I think there will be a lot of manufacturers that follow Apple’s lead—making devices that use the real Web, not some dumbed down version. (Some manufacturers are already doing this, more will follow just to remain competitive.)
The best way to look at the problem is from an information architecture point-of-view (specifically in regard to usability.) From that vantage point, it seems that domains like mobile.domain.com and domain.com/mobile make the most sense. It lets the user get to a part of the site where layouts can be larger and less essential content can be filtered out.