public static function getAll($lastRequestGmt = NULL)
    {
        $countries = array();
        $response = self::getClientInstance()->call("getdidwwpstnrates",
            array('last_request_gmt' => $lastRequestGmt)
        );


        foreach ($response as $countryWithNetworks) {

            $countries[trim($countryWithNetworks->country_iso)] = new \Didww\API2\Country((array)$countryWithNetworks);
        }
        return $countries;
    }