It is possible to install multiple modems on one computer - but you must check with your modem manufacturer that their drivers allow this, you may get Driver Conflicts if you install the modems with the SAME model. These can manifest as the following behaviour of your PC:

• It spontaneously reboots
• It runs noticeably slower
• It fails to Shutdown
• It will not boot
• Windows or software crashes

These are almost never a symptom of a software fault. You can exchange the modem for a different model/revision or for a totally different modem by a different manufacturer.

For professional multiline installations we strongly recommend you consider using a professional telephony card(such as Digi Acceleport Ras 4/8 Port Modem cards,
Dialogic Diva Media Boards 2/4/8 Ports, Mainpine IQ Express 2/4/8 Port Modem,
Multi-Tech MultiModem ISI Multiport Analog Modem and Comtrol RocketModem IV, etc.).