There's a mobile app called Tapatalk which supports vBulletin 4.0.
It makes browsing forums from a smartphone much easier and cleaner. Works with Android, Blackberry, and iPhone.
I'd really enjoy being able to use this, and I'm sure other people would too.
All you have to do is sign up (I provided the URL for admins) and install a plug-in I think. Seems pretty simple, and secure.