Now that I've had a smartphone for a while I'm really beginning to appreciate the sites that have mobile versions. I use the OBS mobile site all the time and it's great. It would be nice if we had a mobile version of the forums as well. There are many, many mobile skins available for vBulletin. I'm not sure which vBulletin version is running here so I couldn't really check for specific ones that would work. The ones that I like the best are those that provide complete navigation and display of forum posts with text wrapped to the width of the mobile device screen so that no horizontal scrolling is necessary. Many provide the ability to post and reply as well along with search, PM, etc. I.e., the most commonly used features.
There seem to be two methods for using these - allowing the user to select a specific styleid to switch to the mobile skin or auto-detect methods (there are several) the detect the mobile device and switch to the appropriate skin automatically.
One option that looks quite good is: http://www.vbulletin.org/forum/showthread.php?t=174375 but there are tons of others. For mobile users out there you can see this skin in action at http://www.byggahus.se/forum?styleid=17. Unfortunately this site is not in English but it was the best working example I could find. You'll get the idea anyway.