Not quite like a regular phone
You can find an in-depth look at makes VoIP tick in the Voice Over IP Need-To-Know. But for those of you who need just the basic VoIP 411, here it is in a nutshell.
In VoIP, phone calls are routed over your high speed cable or DSL (Digital Subscriber Line) Internet connection. In some cases, you'll even be able to use VoIP services with your analog fax machine. With few exceptions, you talk over your regular phone, which is hooked up to your broadband router via a device called an Analog Telephone Adapter, or ATA for short. ATAs convert your voice into packets of digital signals. Unless you are using a browser-based softphone or special VoIP phone, you'll plug your standard phone's analog phone cord into the back of your ATA, and use an Ethernet cable to connect your ATA to your broadband router.
The current crop of ATAs usually have two POTS (Plain Old Telephone Service, i.e. your current phone) RJ11 jacks and can support two different VoIP phone numbers (you pay extra for the second line). Many VoIP service providers also offer the option of including a router with your order, which sometimes has the ATA built-in. An example of this is the Linksys WRT54GP2 available with Vonage and AT&T CallVantage services. Figure 1 shows another configuration, with separate router and ATA.
Figure 1: Setup with Wireless Router and separate ATA
(image courtesy Verizon VoiceWing)
The "Internet Protocol" reference in VoIP describes the way in which packets (small groups of bits and Bytes) are sent and received over the Internet. This packet transfer happens when you download a Web page, or send and receive emails. The process also occurs with calls you make over the Internet, which are translated into packets of data and then re-interpreted back to sounds (and in some cases, video as well) at your recipient's PC.
While this may sound expensive, it isn't. In fact, most of the more than 400 or so VoIP-service providers in North America (which include some traditional phone companies such as Verizon and AT&T) charge either a flat monthly $14.95 to $29.95 fee for unlimited national and some international calling, or assess just a few cents per minute for each call (plus a reduced monthly fee).
There are a couple of drawbacks to VoIP, however. If your cable modem or DSL service goes down, so will your VoIP connection. And although the technology is improving, VoIP services do not work well for emergency "911" calls. That's because your calls are mapped from an IP address for your computer - whether your computer is at your on-record physical address or not. If you take your computer with you, and make a "911" call from it, the emergency dispatcher won't know for sure where you are located.
Another potential problem is that the quality of your call depends not only on your Internet connection, but on what happens to those bits and Bytes as they traverse the wide-reaches of the Internet. The two isssues that are most relevant to call quality are latency and dropped packets.