I have just tested the TouchBB application for the iPhone. The free version only allows you to use 2 forums and your messages will have a message “posted by TouchBB”. However, for € 0,79 you won’t have any of these restrictions. Go and buy it!
For a forum to support this application a plugin needs to be installed. The Homeseer forum has not deployed this plugin yet. So check if your favorite forum supports TouchBB.
Update: It is now a universal application (Google PDF view)