I've just come across the HTTP_PROFILE header that seems to be used by mobile browsers to point to an .xml document describing the device's capabilities.
Doing a Google search doesn't turn up any definitive resources on what this is and how it should be used, can anyone point me to something along the lines of a spec/W3C standard?
I just found this page: http://www.mobileok.kr/eng/develop2/ddrserver.php
It didn't seem to be authoritative at first glance from the search results, but looks like it might be.
I think you may find http://en.wikipedia.org/wiki/UAProf to be of interest?
Device Atlas, Wurfl or TeraWurfl are well worth looking into if you want to do some proper mobile device detection. These provide easy access to device properties so you can use content adaptation techniques to serve pages and content which is carefully optimised for the device being used.