Tom, below is a definition of VoIP. Skype is a program that allows you to use VoIP. My brother called me once on Skype (He's a techie too and was just playing with it), it sounded really good for a computer call. It was a clear conversation, good volume, not quite full duplex, but with only a hint of hesitation.
By the way Vonage is also a VoIP provider, but it takes the place of your "land" line. However, it can cause other problems, such as not allowing your home alarm system to communicate.
Sheri
"Voice over Internet Protocol (VoIP), is a technology that allows you to make voice calls using a broadband Internet connection instead of a regular (or analog) phone line. Some VoIP services may only allow you to call other people using the same service, but others may allow you to call anyone who has a telephone number - including local, long distance, mobile, and international numbers. Also, while some VoIP services only work over your computer or a special VoIP phone, other services allow you to use a traditional phone connected to a VoIP adapter."