This plugin below should be in the core of Joomla:
blog.emandtee.com/2010/04/mobile-content...-page-1/#comment-401
This plugin fills a need in Joomla that isn't currently available. Lets say you designed a page for the desktop user experience which is 960 pixels wide and has a lot of graphical elements. Now when you view this page on your mobile browser you are serving up a mobile template but this page now blows up off the screen and doesn't fit it at all. It is also taking a long time to load because of all of the images. This plugin allows you to use simple tags to switch the content you want to use for the desktop version of your site and the mobile version. Basically you can target the mobile version of the site specifically with more stripped down content that is more usable while keeping the desktop content/design intact. It's a very simple way of implementing a solution to a problem that exists in Joomla right now for mobile.
Since the mobile user experience is very different from desktop because of the small screen/limited space to work with, we need this feature so when we come across a page that won't work on the mobile device, we can just easily use these tags to serve up different content instead. Please consider implementing this plugin into the Joomla core I think its a much needed feature.