This came up as a question at Community Works: How can I translate my blog for mobile devices? Here are some tools for customizing/porting WordPress blogs to mobile devices. Note these are for WordPress.org websites that are installed on your own hosting environment. See What’s the Diff? for full description of WordPress.com v. WordPress.org.
Multiple Mobile Plugins at WordPress.org – http://wordpress.org/extend/plugins/search.php?q=mobile&sort=
Paid plugin that helps you convert to multiple mobile platforms – https://www.bravenewcode.com/store/plugins/wptouch-pro/