Here is what Telegeography has to say on the subject: Computer-based Voice over IP (VoIP) is nothing new, but Skype is the first such service to break into the mainstream, attracting millions of users worldwide. Skype had 1 million simultaneous users within six months of the release of its first version for Windows in July 2004. By the end of the third quarter of 2006, Skype had 136 million registered users, and the number of users online now regularly exceeds 8 million. These users generated about 6.6 billion minutes of traffic in the third quarter of 2006, and are on track to make over 27 billion minutes of PC-to-PC calls this year.