When the arm port is done, it would be nice if there would be a effort to port Haiku to the iphone and similar touchscreen devices. A special touchscreen adapted interface is required and drivers for touch input and accelerators too. A virtual keyboard is easy to make, but handwriting recognition is harder. Maybe a port of a open source handwriting recognition engine can be used to solve that. I really hope that this will become reality soon.
I’ve yet to see Linux run on an iPhone. I’m not saying that it can’t be done for that one but I think for the time being investing resources in porting to such platforms would be to dilute efforts.
We do want Haiku to run on as many platforms as we can but let’s not lose focus here.
While Haiku’s current primary focus is desktops, I do think it has a future on smartphones. I think before closed platforms like the iPhone are targeted some work should be done on more open platforms, such as some of the Android phones or more specifically the Pandora open source hardware platform. Of course the latter has yet to be released and it is becoming a bit like Haiku: a lot of people want it released but it isn’t quite there yet 
Of course before any of this is done Haiku needs to work well on ARM.