From my understanding, any page will work with a small screen device. There are ways of optimizing pages for small screens using CSS and this isnt too hard but as for the forums, they appear to be a bit large for use on a cell.
the only alternative I can see is having a seperate forum which can only be accessed by cell phones and small screens. This would have a reduced number of boards and would not be as active
that does take up more of the server resources though and people on one forum wouldnt be able to see the other
Edit: Opera (the browser) have a small screen mode which renders the page as it would appear on a cell phone or other device.