I have a CSS style on my site with no graphics for mobile users, but I've never done a template layout for small screens. The only problem is detecting the browser that is being used, and then calling a different style sheet in the showflat and showthreaded sripts based on the results (the last part is easy: I do it now for my article templates). It would be better if it can be automatic, so that first time mobile users automaticly get a site formatted for a small screen...
Once I finish the Facelift mod I'm working on I'll look inot doing this one -it's got a lot of "geek factor"
