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/');}?>