I absolutely love VOIP. I use ATT's Callvantage VOIP service and I love it. It provides unlimited local and long distance phone service for $29.99. It uses my internet connection provided by my cable company to provide me with a dialtone. As long as a I have a broadband internet connection I can theoretically plug it in anywhere and be able to use my Voip Service. http://www.callvantage.att.com/
Another Voip Product that I use is Skype. http://www.skype.com
It harnesses the power of my internet connection again. The difference with this is that it uses a software client that connects to a Peer-2-Peer (P2P) Network of Millions of Users. You can dial other Skype users or landline numbers (for a small per minute fee like .02 USD)
Skype in a nutshell.
Our software’s quick and easy to get started with. Download, register, install, plug in your headset, speakers or USB phone and start calling your friends. The calls have excellent sound quality and are highly secure with end-to-end encryption. You don’t even need to configure your firewall or router or any other networking gear. It just, you know… works.
There's a 3rd party hardware program for Skype that allows you to make and answer skype calls on your regular home phone. http://www.echostore.com/skype-phone-adaptor-usb.html
Another product is Free World Dialup (FWD) http://www.freeworlddialup.com/
What FWD Is . . .
FWD is the largest open network service provider for person-to-person, advanced, real-time IP communications.
FWD enables anyone with a broadband connection to communicate by IM, Voice, or Video and share their presence over the internet.