With traditional telephone service, when you speak into the mouthpiece of your phone, the mechanical vibration of the mouthpiece produces a tiny electric current that varies as your voice varies. Electronics in the phone amplifies this tiny signal so it can be sent over the phone wires to the central office in the PSTN (Public Switched Telephone Network). At the earpiece, the reverse happens: a continuously-varying electrical signal is turned into mechanical movement of the earpiece diaphragm, which reproduces the sound.

This sequence of soundà electricity and electricityà sound is called an "analog" process and we refer to telephones as analog devices. In traditional phone service, the signal is analog from end to end, meaning that a continuously varying electrical signal travels from your phone to your local phone company central office, then possibly to one or more additional central offices and finally to the destination telephone. (This is something of an oversimplication of reality, but I'm trying not to confuse the reader too soon into the article --there'll be time to confuse you thoroughly later on!)

Historically, the wires that carried this signal belonged to the appropriate local phone company at the originating and destination end of the call and possibly to one or more long distance carriers in between. Before the breakup of THE phone company in 1983, one company, AT&T, owned nearly all this infrastructure, with a few tiny independent phone companies thrown in and a handful of large alternative long distance companies, mostly providing services to large business enterprises.

Even recently, the local telephone wire going into most homes and offices belongs to the local phone company. However, competition for telephone customers has led to the phone company in each region renting out their facilities to process calls through other providers. This increased competition has set the stage for new and different waysto carry phone calls.

With the explosion of computer use in America (and, indeed, around the world) engineers have come up with faster and better ways to connect your PC to the internet. These "broadband" services allow your computer to be always connected - without the cumbersome, slow, and often malfunctioning dial-up process - and they also provide much greater speed than dialup.

Even before broadband, people realized that, if you could figure out a way to talk through your computer and someone on the other side of the world did the same thing, you could theoretically talk with them using your internet connection at no extra charge. And, since many computers include speakers and a microphone, it wasn't too hard to see how this might be possible. And it was also pretty obvious that it spelled F-R-E-E long distance calling - or very nearly free, as we shall see in a moment.

But how many people had their PCs setup to do this? And what if you wanted to talk to someone who didn't have a computer? And what about local calls? Was there a way to eliminate the expense of the monthly phone bill, just for the privilege of being connected to the public telephone network? These and other questions have driven a lot of engineering and marketing development in the last few years and the ongoing result is VOIP.

VOIP stands for Voice over internet Protocol, a fancy way of saying, "let's send phone calls over the internet." Remember the analog process described at the beginning of this article? Well, VOIP replaces some or all of that with a digital process where digitized voice data is mixed in with all the other digital data and routed over the internet.

For the simplest form of VOIP, let's take a look at home and small-office phone service being offerred by cable companies, such as Time-Warner, Comcast, and others. If you already have broadband internet service coming into your home or office from your local cable company, they may be able to offer you a type of VOIP phone service over the very same connection that you use to browse the web. In such an arrangement, the cable company replaces your data-only cable modem with a unit that also includes one or more phone jacks.

You can plug any ordinary analog phone into this jack. At the telephone, the sound à electricty and electricty à sound process is still analog, but, once the signal enters the cable modem, it is turned into digital data and carried by the cable company's network to the central office nearest the destination, where the call is then handed off to the local phone company at the destination. But, except for that local piece, the call was handled almost entirely over the internet. And usually for a flat monthly cost that is often less than your phone company's monthly service.

The benefits of this approach versus using two computers with microphone and speakers are obvious:

• You can call anyone, whether or not they have a computer, because the VOIP provider (your cable company in this discussion) interfaces (connects to) the PSTN (remember the PSTN - that's the public telephone network).
• Many of these services allow unlimited calling, even long distance, and international rates so cheap they will make your eyes pop out.
• Calls made computer-to-computer (where the PSTN is not involved) may even be completely free, as is the case with SKYPE service.