vBulletin is now pushing their mobile suite, which lets you develop your own iPhone and Android apps.
Mobile access for community members is getting very important. IMO, the traditional browser, even with a mobile-friendly skin, is losing out to dedicated apps. I introduced mobile apps on a busy forum a few months ago and was really surprised at the volume of usage.
If you try the vB mobile app, be sure to post here and tell us how it worked!