I've found a Web site that lists all the VoIP providers in the world, country by country.
The site is called VoIP Providers List, and I've just linked you to there.
When I last checked earlier today, they had 1003 providers listed in 102 countries from Afghanistan to Yugoslavia. Who knows, maybe Osama is on Kandahar-based IIA (Internet In Air). Then,probably not.
More important for U.S. users, the site lists 320 U.S.-based VoIP providers. Not only their URLs, but pages full of everything you'd want to know about each.
Let'stake this baby out for a spinand you'll see what I mean. Randomly, I clicked on the link to the information page for Ionosphere, Inc.,a diversified VoIP services provider in Greenville, S.C. I see a list of what they offer, the equipment that they use, and even contact info for their marketing person.