If you ever had any doubts about the increasing popularity of VoIP, the most recent information coming out of Skype will dispel them. The company's user base is growing very rapidly, with an estimated 380,000 new users signing up every single day. Those numbers are astounding, almost unreal - I'm skeptical myself as to how accurate that is. If they really are getting more than a third of a million new customers every day, it's unlikely they can carry that momentum for long, but nevertheless it demonstrates that the company is doing very well with them sitting on a user base that is 405 million strong.
There's no detailed usage statistics along with those numbers other than the company's claims that nearly a third of its registered subscribers now use Skype for business purposes. The increasing number of PDAs and other devices that have Skype clients is helping them, and the service itself is now representing around 8% of the international calls made worldwide.
Skype just recently introduced version 4.0 of their Windows client, which brought with it an interface revamp and improved video quality. The new client has great improvements to usability, which should help them get and retain those mass amounts of customers.