public function deleteContact($contactId)
    {
        if (is_null($contactId) || $contactId == '') {
            throw new Exception('The contactId is required to delete a contact.');
        }

        $params = array(
            'method' => 'sp.contact.delete',
            'contact_id' => $contactId
        );

        return $this->_makeApiRequest($params);
    }