Known as "VoIP" in phone circles — short for Voice over Internet Protocol — it is the latest iteration of the communications revolution that began with Bell's telephone in 1876. Now VoIP, a 20-year-old technology, seems poised to become a fixture in the lives of millions of Americans.

"VoIP is at an inflection point where it's about to go mainstream," says Phil Asmundson, vice chairman and a U.S. managing partner, technology for Deloitte & Touche.