Load a different WordPress theme for mobile visitors

unplugged-plugin.php

<?php
/*
Plugin Name: Unplugged Mobile Theme
Plugin URI: http://www.rachelbaker.me
Description: A plugin and theme for WordPress that automatically reformats your blog's content for optimized viewing on Apple's <a href="http://www.apple.com/unplugged/">unplugged</a> and <a href="http://www.apple.com/ipodtouch/">iPod touch</a>.
Author: Rachel Baker
Version: 0.1
Author URI: http://www.rachelbaker.me

# Special thanks to Imthiaz Rafiq and the wp-pda Plugin (http://imthi.com/wp-pda/) which this plugin is derived from.

# This plugin is free software; you can redistribute it and/or
# modify it under the terms of the GNU Lesser General Public
# License as published by the Free Software Foundation; either
# version 2.1 of the License, or (at your option) any later version.
#
# This plugin is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this plugin; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

*/

class UnpluggedMobile{
	var $unplugged;

	function UnpluggedMobile(){
		$this->unplugged = false;
		add_action('plugins_loaded',array(&$this,'detectunplugged'));
		add_filter('stylesheet',array(&$this,'get_stylesheet'));
		add_filter('template',array(&$this,'get_template'));
	}

	function detectunplugged($query){
		if(preg_match('/(alcatel|amoi|android|avantgo|blackberry|benq|cell|cricket|docomo|elaine|htc|iemobile|iphone|ipad|ipaq|ipod|j2me|java|midp|mini|mmp|mobi|motorola|nec-|nokia|palm|panasonic|philips|phone|sagem|sharp|sie-|smartphone|sony|symbian|t-mobile|telus|up\.browser|up\.link|vodafone|wap|webos|wireless|xda|xoom|zte)/i', $_SERVER['HTTP_USER_AGENT'])) {
			$this->unplugged = true;
		}
	}

	function get_stylesheet($stylesheet) {
		if($this->unplugged){
			return 'unplugged-mobile-theme';
		}else{
			return $stylesheet;
		}
	}

	function get_template($template) {
		if($this->unplugged){
			return 'unplugged-mobile-theme';
		}else{
			return $template;
		}
	}
}
$wp_unplugged = new UnpluggedMobile();
?>