The using the user agent function of PHP is there an easy way to serve up custom style-sheets and Smarty Templates based on what device their using: eg a mobile device vs laptop/desktop.
The user agent will tell you what device the user is using. You could use something like http://mobiforge.com/developing/story/lightweight-device-detection-php or http://detectmobilebrowser.com/ to detect what kind of device is being used and then serve the corresponding smarty template