Cant say I've ever tried using the blackberry for the forum, I did try getting on the SBK site while at one of the superbike race days and just left the device downloading for ages.
I think the site is to graphical (avatars) for a Blackberry and would take to long to load. I know some Bulletin Boards have a pda/mobile device version of the forums.
Maybe a different theme needs installing that doesnt use graphics on the forum ? But that would be a job for the webteam.
Rich.