Modem Operation A-7
Hanging up
To disconnect the modem from the phone line, type +++ to enter
command mode, then type ATH and press the Return key.
Clearing the command buffer
The command buffer acts as memory, storing up to 40 command
characters in a single command line. If you get an ERROR response,
try typing AT to clear the buffer. The ISDN modem should return the
OK response indicating that it is ready for new commands.