Mobile Domain plugin by byoozz will redirect your blog to a mobile domain when visitors come to your blog from a mobile browser, when visitors visit your mobile domain, they can switch it to the desktop domain anytime. You can select your mobile themes to be different from the desktop-themes. If your wordpress installation is in the subdirectory, this plugin will automaticaly detect it.
If you access the wp-admin from mobile domain, this plugin will automaticaly redirect it to the desktop wp-admin.
Download: http://wordpress.org/extend/plugins/mobile-domain/