Mobile Client Detection Plug-in for WordPress by Martin Zeitler provides query_vars ‘platform’ & ‘browser’ for simply switching the layout within your site.
The author says “This plug-in provides the required variable for serving a customized version of your theme!!
Currently it can detect the following user-agents: Android, Blackberry, iPad, iPhone, iPod, IE mobile, webOS and even GoogleBot mobile.
Beside that it can detect various desktop platforms & browsers – so it’s quite handy for fixing things for specific user-agents (instead of using conditional CSS).”