You would probably be better off using css media queries to pick a mobile.css file rather than the style.css. I'm working on such a project for my personal installation of OST. Once I complete the job, I will be releasing it onto the forums, but it could be a few months.
If you want to start working on something like this yourself, take a look at this website for a quick introduction to media queries. http://www.alistapart.com/articles/responsive-web-design(http://www.alistapart.com/articles/responsive-web-design)
My plan is to actually, not just make a mobile version of OST, but completely make it a responsive website.