docs: synchronized void hungup(Date dateOfRemoval, HangupCause hangupCause, String hangupCauseText)
      {
          this.dateOfRemoval = dateOfRemoval;
          this.hangupCause = hangupCause;
          this.hangupCauseText = hangupCauseText;
          // update state and fire PropertyChangeEvent
          stateChanged(dateOfRemoval, ChannelState.HUNGUP);
      }