Redirect Mobile Devices with PHP

<?php
$android = strpos($_SERVER['HTTP_USER_AGENT'],'Android');
$ipod = strpos($_SERVER['HTTP_USER_AGENT'],'iPod');
$iphone = strpos($_SERVER['HTTP_USER_AGENT'],'iPhone');
$palmpre = strpos($_SERVER['HTTP_USER_AGENT'],'webOS');
$berry = strpos($_SERVER['HTTP_USER_AGENT'],'BlackBerry');

if ($iphone || $android || $palmpre || $ipod || $berry == true) 
{ 
header('Location: http://mobile.web.com/');
}
?>