Probably a better method is to make use of a WURFL. Unfortunately in WB the best way I can think of for doing this is either to create a separate subdomained site for each mobile template that you provide (i.e. basic, intermediate, advanced), or alter the php in the template for your subsite differentiate. Either way you'd have at least two separate sites. A CMS that stores all the content (without pagename.php files) in the DB would be a better choice for full mobile templating.
http://wurfl.sourceforge.net/http://www.tera-wurfl.com/wiki/index.php/Main_Pagehttp://www.mobilejoomla.com/