skype, the free VoIP-based service for PC to PC phone calls, claims it has had 100 million downloads. it is fast becoming the gold standard for voice-over-IP, and the few times i have used it, i have not been disappointed: it seems better than other services i have used in the past. of course, the advantage is that it costs you absolutely nothing to talk to someone else on a PC anywhere in the world: the only requirement is a broadband internet connection and a headset/mike combination at both ends.
they also offer PC to landline calls at some 2 cents a minute. i have never tried it. they have also now started a mechanism landline to PC calls. some entrepreneur is planning to also offer mobile-to-skype calls, i just read about it somewhere.
this skype thing could become a phenomenon.
the founders of the scandinavian company were those behind kazaa, the peer-to-peer music and file downloading software.