If you do, dont forget about the Palm Pre.
I own a Palm Pre (not an iPhone) but from what I've dabbled with, the SDK's are similar enough that coding for both would be relatively simple. Having said that, the company that designs and maintains UBB threads is going through some changes (all good from what I've read) and is planning a major software release (date TBD). The changes I read about will make viewing much easier on the current and future generation of web enabled phones like the Pre and the iPhone.
In the mean time, what kind of functionality would you be looking for from an app?