code: func (c *Call) Ended() bool {
  	// https://www.twilio.com/docs/api/rest/call#call-status-values
  	switch c.Status {
  	case StatusCompleted, StatusCanceled, StatusFailed, StatusBusy, StatusNoAnswer:
  		return true
  	default:
  		return false
  	}
  }
docs: // Ended returns true if the Call has reached a terminal state, and false
  // otherwise, or if the state can't be determined.