public static function getAll($iso = NULL)
    {
        $countries = array();
        $response = self::getClientInstance()->call("getdidwwcountries", array('country_iso' => $iso)
        );
        foreach ($response as $c) {
            $country = new Country((array)$c);
            $countries[$country->getCountryIso()] = $country;
        }
        return $countries;
    }