public function transfer($phone, $args = array() /* polymorphic */)
    {
      $url = URIResource::Make($this->path, array($this->id));
      $data = Ensure::Input($args);
      $data->add("transferTo", (string) $phone);
      $data->add("state", CALL_STATES::transferring);

      $response = $this->client->post($url, $data->get());
      
      $id = Locator::Find($response);

      $data->add("id", $id);

      return Constructor::Make($this, $data->get());
    }