A high-speed serial port is essential for using a 14,400 bps or faster modem. If you know how to use the diagnostic tools on your computer, you can check for a UART chip that is listed as 16550 xx, where xx is either blank or a series of letters. If you own an older PC such as a 486 computer and even an early Pentium, the UART chip may not be a 16550. If the UART is an 8250, your high-speed connection will not work reliably. Look for a warranty of at least 12 months, parts and labor.
Warranties vary from manufacturer to manufacturer, but usually run one, three, or five years.
Check with the salesperson before you buy, or refer to the vendor's Web site for further information. We recommend you purchase an established name-brand modem, like Megahertz, US Robotics, Hayes, Dayna, etc. The Support Center staff has encountered many such problems firsthand. In general, videoconferencing is still an emerging technology. Also note that you can purchase a new product with great software, but will likely be limited to communicating with those who have the same software.