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.
You have the option of viewing this site in both "mobile" and "full site" modes/skins/styles.
Scroll down towards the bottom of the page, past your posting permissions, and you'll see a darker ribbon that has links on the right hand side and a drop down menu on the left that will allow you to switch from full to mobile.