Only windows mobiles can run V-Planner which limits you to the HTC type phones (o2 orbit, T-Mobile Vario, TyNc -all the same rebranded phones). Which are pretty good btw - do everything you need them to do, but are a little bit brick like. However, mine has been repeatedly dropped onto concrete and still works
The LG Viewty is Java enabled, so you can put something like JDeco on it. I think this is a pretty good phone so far, installed the Opera mini web browser on it because it's better than the standard one.
Think there's a new Sony phone due out that will have Windows on it.