var
hCommFile: THandle;

procedure TForm1.Button1Click(Sender: TObject);
var
PhoneNumber: string;
CommPort: string;
NumberWritten: LongInt;
begin
PhoneNumber := 'ATDT 1-555-555-1212' + #13 + #10;
CommPort := 'COM2';
{Open the comm port}
hCommFile := CreateFile(PChar(CommPort),
GENERIC_WRITE,
0,
nil,
OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL,
0);
if hCommFile = INVALID_HANDLE_VALUE then
begin
ShowMessage('Unable to open ' + CommPort);
exit;
end;

{Dial the phone}
NumberWritten := 0;
if WriteFile(hCommFile,
PChar(PhoneNumber)^,
Length(PhoneNumber),
NumberWritten,
nil) = false then
begin
ShowMessage('Unable to write to ' + CommPort);
end;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
{Close the port}
CloseHandle(hCommFile);
end;