If there is an add-on (or someone builds one) to expose a more complete set of functions for reading and posting, it would be quite easy to build an iPhone app around it. (I didn't just volunteer to do write the iPhone app, did I? I already have two semi-active iPhone development projects.)
Obligatory old man complaint: Of course, one could also just make phpbb do something crazy like implement NNTP, a protocol designed to allow various applications running on client systems to efficiently browse a shared repository of messages divided up into groups and threads. It's the sort of crazy thing we did 20 years ago before someone decided to do it the hard way by putting a browser in the way and calling newsgroups "forums."




