Today I was confronted with one of those pop-up web ads like the kind they use to sell those X10 Tiny Wireless Cameras on almost every big web site out there. Except this one was a little different. This product said that without buying a second telephone line, it would let you talk on the telephone and be online at the same time.

Now, having played with dial-up modem systems all through my childhood, this very concept was fascinating to me. What sort of magical device could maintain an Internet connection on an analog modem and allow the user to carry on a voice conversation at the same time?

So I clicked on the ad...1

Now you always get the call – even while browsing the Internet! With Catch-A-Call, there’s no more frustrating busy signals for friends and family trying to reach you… no more rushing the kids off the computer to free up your phone line… and no spending money to install (and pay monthly fees for) a second phone line.

Catch-A-Call even lets your PC share a phone line with a fax machine! And when you get a phone call while online, you can talk as long as you’d like without getting disconeected from the Net! Compact unit measures just 4 ¼” x 3 ¼” x 1”. Features include:

(Requires Call Waiting service from your local phone company)

There were two main concepts I had trouble with. The first was "no spending money to install a second phone line. . ." This reinforced their earlier claim, and was backed up by the disclaimer that the device "Requires Call Waiting service."

This second line was what I really couldn't understand: "you can talk as long as you’d like without getting disconeected from the Net." In order to be online "as long as you'd like", your modem would have to communicate some sort of carrier signal longer than the timeout settings of the modem. It would be very difficult to simulate this without making for a very awkward telephone conversation.

A Google search on this device pulled up 30 or 40 other cheap merchandise peddlers with the same ad content (an extra superlative here and a paraphrase there). But I found my answer in a product review on

The reviewer wrote that this call-waiting modem isn't a new concept, although I'd never heard about it. I must have gone digitial before it became a serious consumer item feature. But anyway, he writes:3

Special call-waiting modems are available that allow you to hear a call-waiting tone while you're online and accept the incoming voice call. Rather than buy a new modem when you've got a perfectly good one installed in your computer right now, use International Electronics' (IEI) Catch-A-Call.

Essentially what the box does is overhear your modem's conversation to the ISP. When it recognizes a call-waiting tone, it will make a small ringing sound. Okay, so far so good. You don't have to miss a call if you're on the modem. But how can you stay online "as long as you'd like", and still talk to your friends on the phone? Again, from the review:

To compensate for the lack of reliability of Caller-ID during Call Waiting, Catch-A-Call offers a terrific feature. It allows you to pick up the phone when you're online, automatically putting the Internet on hold. The length of time you'll be able to pause your Internet connection varies according to your modem, PC settings, and telephone company. We were able to do so for about eight seconds, long enough to identify the caller. IEI offers a method of extending that time. From the Start menu, select Settings/Control Panel/Modems, and highlight your modem on the list (if more than one is listed). Next, select Properties/Connection/Advanced, and enter "S10=255" in the Extra Settings window.

This is pretty much what I had assumed. "As long as you'd like" better be within 8 to 255 seconds, or one of the two communicating modems will decide that the silence on the other end means that there won't be any more data coming over the line after the timeout and give up the connection. Then you'd have to redial.

I expect that this would probably wreak havoc with stateful Internet services like AOL Messenger and any open telnet sessions after about 120 seconds or so, depending on your TCP packet timeouts.

So it's not perfect, but I didn't expect that. It is falsely and misleadingly advertised, and may not be quite the amazing contraption consumers had hoped at the $50 price tag.


1. Source:,
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3. Source: Bedford Communications Online,,