UPDATE: Please use the
http://wordpress.org/extend/plugins/wordpress-mobile-pack/ plugin instead, here's a brief description of the new plugin:
The dotMobi WordPress Mobile Pack is a complete toolkit to help mobilize your
WordPress site and blog.
It includes a mobile switcher to select themes based on the type of user that
is visiting the site, a selection of mobile themes, extra widgets, device
adaptation and a mobile administration panel to allow users to edit the site
or write new posts when out and about.
Please don't use this version of the plugin any more, either swap to or try
out the dotMobi mobile plugin:
http://wordpress.org/extend/plugins/wordpress-mobile-pack/