Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 21074)
+++ wp-includes/functions.php	(working copy)
@@ -3685,14 +3685,8 @@
 	if ( ! wp_is_mobile() )
 		return true;
 
-	$ua = $_SERVER['HTTP_USER_AGENT'];
+	$regex = '#(iPod|iPad|iPhone); U; CPU( iPhone)? OS ([\d_]+) like Mac OS X#';
 
-	if ( strpos($ua, 'iPhone') !== false
-		|| strpos($ua, 'iPad') !== false
-		|| strpos($ua, 'iPod') !== false ) {
-			return false;
-	} else {
-		return true;
-	}
+	return ( preg_match( $regex, $_SERVER['HTTP_USER_AGENT'], $version ) && version_compare( '6', $version[3], '<=' ) );
 }