be available on hand;be at sb’s beck and call; be on call at any hour stay within call
❍ 他答应～，绝不延误。He promised to be on call at any hour and would never delay for any moment.
随叫随到suí jiào suí dào
形容人很勤快，随时传喊，随时来到。be on call at any hour, on call, be brought up to some place at any hour, at call