Question: What's the word on dual-line modems? Don Wendel <donwendel@mindspring.com> wrote in wondering about dual-line modem technology.

Answer: Dual-line modems use two phone lines and two internal modems to double the speed of your connection, theoretically approaching that of ISDN service. Both Boca Research and Diamond Multimedia have shipping products, but few ISPs have set pricing yet on how they'll support this new hardware.

<http://www.bocaresearch.com/docs/mddl56i.htm>
<http://www.diamondmm.com/shotgun/>

Because these modems use two phone lines, you wind up paying the phone company twice. But when you compare residential phone line costs - which are usually unmetered in the U.S., meaning you pay a fixed monthly rate - to ISDN costs, two residential phone lines are usually cheaper. In Seattle, for instance, two phone lines are about $55 per month with tax, while unlimited ISDN is about $80 per month with tax. (In some areas, ISDN service is metered, so costs can be even higher; in others, ISDN is as little as $25 per month for unlimited use.)

Both Diamond and Boca's devices allow you to subscribe to call waiting so that if you're connected on both lines, an incoming call will be passed through on one without disturbing your Internet connection. Diamond's technology can be set to add the second phone line automatically when traffic becomes heavy instead of using both lines at all times.

Diamond's Web site notes that they are building dual-modem technology into the entire Supra line so that you'll be able to buy any two Supra modems and get dual-line functionality.

Pricing for service will be interesting, because the cost to an ISP could be double, and it seems likely that someone with one of these devices will spend more time online. [GF]