If you would like to connect to the Internet or send and receive E-Mail, you need a modem.
A modem is a unit which translates data into sound and transmits it over the telephone wire to another modem which in turn translates the sound back into data so they can be displayed on you computer.
There are external as well as internal modes available. The internal ones are installed inside your computer and the external ones are connected to your computer by a cable. Most widely used modems today provide for speed of 56.6 Kilobytes per second for transmission from computer to computer and a maximum speed of 14.4 for fax transmission.
If you have a good modem together with a good computer fax software, you do not need a fax machine. As a matter of fact, the cost for modem and software is far less than the cost for an equally sophisticated fax machine.