As Quicknet was the first and as of this writing (March 7, 2000) the only maker of VoIP hardware that released Linux drivers under GPL terms, my choice was fairly straightforward. In January 2000, I paid $159 for a PhoneJACK-PCI. It's a sparsely populated short PCI card, with a pair of audio connectors (mic/ear) and a single phone socket (RJ11). Here's a quote from Quicknet's HOWTO:
These cards offer nice telco style interfaces to use your standard telephone/key system/PBX as the user interface for VoIP applications. The Internet LineJACK also offers PSTN connectivity for a single line Internet to PSTN gateway. Of course, you can add more than one card to a system to obtain multi-line functionality. What they mean here is that they have two cards: PhoneJACK has one socket into which you can plug in a standard telephone set. I used a $15 one, and that was it. You can also connect it as one of the incoming ``trunk connections'' on your multi-line telephone system or even a PBX, to build a more ``business''-oriented system.
WARNING! DO NOT CONNECT THIS SOCKET TO THE INCOMING TELEPHONE LINE FROM YOUR TELCO! IT WILL FRY YOUR PHONEJACK AND VOID THE WARRANTY.
Their so-called LineJACK model (ISA only at the moment) at almost twice the price has a second socket which can accept an incoming phone line; with this card you effectively create a two-line phone system for your telephone: one line is the VoIP one, one line is POTS1. That would not be worth much in itself (a two-line telephone set would do the trick for much less), except it allows you to create a link between VoIP and POTS worlds, in effect, a gateway between the two. If you have one of these in a remote location, you can then make the long-distance part of the call go over VoIP and then switch over to POTS for the local part of the call. Most of the PBXs have that function as well, so if you are adding a VoIP link to an existing PBX-based telephone infrastructure, the plain PhoneJACK will suffice, but if you need to upgrade the telephone equipment as well, LineJACK may have the extra functionality that is worth considering. I did not, so there'll be no further mention of LineJACK in this document.
WARNING! DO NOT CONNECT THE PHONE SET SOCKET ON THE LINEJACK CARD TO THE INCOMING TELEPHONE LINE FROM YOUR TELCO! IT WILL FRY YOUR LINEJACK AND VOID THE WARRANTY.
In the spirit of simplicity of the interface: `lift the receiver, press a sequence of keys, hear rings, etc.' I played only minimally with the audio connectors; I found that a $5 headset with a microphone hanging in front of my face produced the sound quality somewhat superior to that of a regular telephone receiver. Clearly, one can also use these connectors to create a speakerphone, or connect to your audio card and mix it with background music, or whatever.
I am happy with PhoneJACK's out-of-the-box performance, the echo cancellation and silence suppression are fairly aggressive, and the resulting bandwidth use is fairly low2. Only one word of caution: the card seems to be seriously (driver installation causes a kernel panic) incompatible with Creative Labs' Soundblaster Live! card, but luckily I was able to make it work by reversing the order of cards on the PCI bus, with the Soundblaster Live! card being the last one. It is possible that the problem is not with the PhoneJACK card, but rather with Soundblaster Live! I have not experienced problems with other Soundblaster (Creative brand name or ASUS compatible) cards.