The Mobile Client Detection Plugin can overload platform-specific themes or templates - and it provides query_vars platform & browser.
In case the mobile version of your blog shall have a different layout or when it’s required to load different versions of CSS/JS code.:
This plug-in can overload template files and theme directories - by the detected platform.
And it can provide query_vars 'platform' & 'browser' for creating multi-device templates.
Currently it can detect the following mobile platforms: Android Phones (Android 1.x & 2.x), Android Tablets (Android 3.x & 4.x), Blackberry, iPad, iPhone, iPod, IE mobile, Kindle, SymbianOS, PalmOS, webOS, GoogleBot mobile.
It also can detect several desktop platforms (e.g. Internet Explorer) so it's quite handy for fixing things for specific user-agents (instead of using conditional CSS).
Please be aware the this is a support plug-in, not a fully featured mobile theme.