You should grab the code from 2.0 which also handles Android and isn't Apple-specific:
$lowres_ua = array("iPhone","iPod", "iPad", "Android");
foreach($lowres_ua as $useragent)
if(strstr($_SERVER['HTTP_USER_AGENT'], $useragent))
$g['theme'] = empty($g['theme_lowres']) ? "pfsense" : $g['theme_lowres'];