mysite_is_mobile..php

<?php 

function mysite_is_mobile()
{
    $isMobile = preg_match("#(ipod|iphone|android|opera mini|blackberry|pre/|palm os|palm|hiptop|avantgo|plucker|xiino|blazer|elaine|iris|3g_t|windows ce|opera mobi|windows ce; smartphone;|windows ce; iemobile)#i", $_SERVER['HTTP_USER_AGENT'] );

    // If an IP is X then show mobile (good for debugging m site)
    // if( $_SERVER['REMOTE_ADDR'] == 'xxx.xxx.xxx.xxx' )
    //    return true;
     
    return $isMobile == 1 ? true : false; 
}