I know this probably isn't a huge priority, but if you could add a wap friendly theme. I like to surf forums on my phone when I'm stuck somewhere waiting, I know, I'm a dork.
I have no knowledge of the WAP system, and I don't know how customizable phpBB is in that regard. The main problem, I'm guessing, is that phpBB's HTML coding is quite awful judging by today's standards. If you know of any phpBB theme that fixes this, let me know.