Tom,

The built-in mobile functionality in DNN helps you to create redirection rules to route mobile device users to a specific page on your site or to a totally different site (such as a dedicated mobile site). It also allows you to create site-groups for single-sign-on + cross-site-module-sharing.  Neither of these is what your question was about... just giving you some insight into some of the mobile capabilities within DNN.

In order to show/hide various panes in your skin you'll need to update the skin's .ascx file and the skin's .css file at minimum. Essentially you'll add a media query to the .ascx file to determine the width of the viewport that's viewing your site and then you'll point to various styles in your skin's css file based on the media query results.

Amelia Marschall Miller from Gravity Works has presented several times on making skins responsive. You should check out here slides on how to make a site responsive. You can find the slides here:  http://www.slideshare.net/gravitywork...

as well as checking out this video where she walks through the process:

http://www.dnnsoftware.com/Community/... 

Hope this helps!