Now you can continue using vbulletin3 for many years to come,we have produced a dekstop theme which is responsive in nature, fully mobile support that will make your forum look very nice in mobile devices.
This style is not a separate desktop and mobile style. It is single style, it will fall into responsive mode when in mobile.
I have made responsive in many pages beside of main pages. Pages include usercp, faq, pm, user online, search results, advance search and many more.
It also supports big images preview in postbit, bb code html, bbcode quote and attachment. All will look good in postbit.