Linux supports dial-in service. This means that you can call in from another computer and log in over the phone. If you have two modems and phone lines for your computer, you can log in and then either dial out on the spare phone line or use Internet services if the spare line maintains an active Internet connection.
Setting up Linux for dial-in service requires the following:
An incoming phone line
A serial port and attached modem
It also requires that you do the following:
Configure the modem.
Edit the system initialization table.
Serial port technical details
For technical information regarding Linux and serial ports, see the Serial-HOWTO and Serial-Programming-HOWTO, often under the /usr/doc directory. ...