protected function renderFile($_sfFile)
 {
     $info = pathinfo($_sfFile);
     $base = "{$info['dirname']}/{$info['filename']}";
     $filename = $base . ucfirst(strtolower(sfJpMobile::getCarrierName())) . '.' . $info['extension'];
     if (!is_readable($filename)) {
         $filename = "{$base}Mobile.{$info['extension']}";
         if (!sfJpMobile::isMobile() || !is_readable($filename)) {
             $filename = $_sfFile;
         }
     }
     return parent::renderFile($filename);
 }