CONST
  STATE_NONE             = 0;
  STATE_INITIALISEMODEM  = 1;
  STATE_BEGINWAITING     = 2;
  STATE_WAITINGFORCALL   = 3;
  STATE_CALLDETECTED     = 4;
  STATE_CALLINPROGRESS   = 5;
  STATE_ENDCALL          = 6;
  STATE_CALLDISCONNECTED = 7;

state:=STATE_INITIALISEMODEM;
nextState:=STATE_NONE;

while (1=1) do
begin
  case state of
    STATE_INITIALISEMODEM : begin
      modem.initialise;
      nextState:=STATE_BEGINWAITING;
    end;

    STATE_BEGINWAITING : begin
      modem.waitForCall;
      nextState:=STATE_WAITINGFORCALL;
    end;

    STATE_WAITINGFORCALL : begin
      if (modem.signalRingIndicator) then
      begin
        nextState:=STATE_CALLDETECTED;
      end;
    end;

    STATE_CALLDETECTED : begin
      modem.pickup;
      nextState:=STATE_CALLINPROGRESS;
    end;

    STATE_CALLINPROGRESS : begin
      if (not modem.signalCarrierDetect) then
      begin
        nextState:=STATE_CALLDISCONNECTED;
      end
      else
      begin
        if (modem.dataReady) then
        begin
          command:=modem.readString;
          processCommand(command,quit);

          if (quit) then
          begin
            nextState:=STATE_ENDCALL;
          end;
        end;
      end;
    end;

    STATE_ENDCALL : begin
      modem.hangUp;
      nextState:=STATE_INITIALISEMODEM;
    end;

    STATE_CALLDISCONNECTED : begin
      nextState:=STATE_INITIALISEMODEM;
    end;
  end;

  if (nextState<>STATE_NONE) then
  begin
    state:=nextState;
    nextState:=STATE_NONE;
  end;
end;