public function getSmsCampaignCost(array $params, array $additionalParams = null)
    {
        if (!isset($params['addressBookId']) && !isset($params['phones'])) {
            return $this->handleError('You mast pass phones list or addressbook ID');
        }

        if ($additionalParams) {
            $params = array_merge($params, $additionalParams);
        }

        $requestResult = $this->sendRequest('/sms/campaigns/cost', 'GET', $params);

        return $this->handleResult($requestResult);
    }