select * from web_adm_gateway_concurrent_calls_start_value('2012-01-01 00:00:00'::timestamptz);

CREATE OR REPLACE FUNCTION web_adm_gateway_concurrent_calls_start_value(p_date_start timestamp with time zone)
  RETURNS bigint AS
$BODY$
    DECLARE i_count integer;
BEGIN

    i_count := (SELECT COUNT(*) FROM cdr
            WHERE p_date_start BETWEEN sqltime AND sqltime_end
            AND gateway_id IS NOT NULL);

    RETURN i_count;
END;
$BODY$
  LANGUAGE plpgsql;

SELECT COUNT(*) FROM cdr
            WHERE '2012-01-01 00:00:00'::timestamptz BETWEEN sqltime AND sqltime_end
            AND gateway_id IS NOT NULL