Note: This plugin is no longer maintained. While it should technically still work, it is a product of its time. If you are considering using this plugin, the modern best practice is to use responsive web development.
This is a WordPress plugin that will detect mobile devices and redirect the user. You just have to tell it where you want the mobile device to go. This plugin does not turn your current site into a mobile site, it directs the user to another url or subdomain where you have mobile content. This plugin is also for self-hosted WordPress installations.
If you want to get the code check it out at https://wordpress.org/plugins/mobileesp-for-wordpress/
This plugin uses the MobileESP detection script (under Apache License 2.0) and is based almost entirely on the Mobile Device Detect plugin by Matthias Reuter