function getContacts($page_index = 1, $page_size = 100, $standard_fields = array(), $custom_fields = array())
    {
        $queryParameters = array(
            'page_index' => $page_index,
            'page_size' => $page_size,
            'standard_field' => $standard_fields
        );

        $queryParameters = $this->appendArrayFields($queryParameters, 'custom_field', $custom_fields);

        return $this->get('contacts', $queryParameters);
    }