I'm sitting in Abu Dhabi, in the United Arab Emirates. I just spoke with my girlfriend in New York for an hour. Per-minute cost: $0. That's because my trusty Internet phone came along with me.
An Internet phone is nothing more than an inconsequential-looking electronic adapter with blinking lights on the front and a few jacks in the back. Plug a normal telephone into its phone jack, then plug the adapter directly into your router, which is hooked up to a broadband Internet connection. Some Internet phone carriers also let you make calls through your computer; others, like Skype, require it. But the genius of most Internet phones is that your computer isn't involved at all.
Increasing competition from tech upstarts like Vonage and anxious traditionalists like Verizon has led to insanely low prices for VoIP (voice over Internet protocol) service. For flat rates as low as $20 per month, you can get a U.S. phone number with unlimited domestic calling—and several services also throw in Canada and parts of Latin America, Asia, and Europe, too. Moreover, because the little Internet phone adapters plug into any broadband Internet connection, your beloved 212 number will follow you to Abu Dhabi.
Source : http://www.slate.com/articles/technology/webhead/2005/06/smooth_operators.html