There's a half-year long thread in Skype Forums, asking "How many different countries will respond to my call?" It's been going on and off for the past seven months and already counted most of the countries there are. But there's always room for more

Regardless of the fact that Skype has different levels of activity in different countries and parts of the world, it's still truly global. Skype is everywhere where Internet is. With wireless, mobile and satellite networks, this means pretty much every bit of land and sea on Earth, and even beyond (we've heard about Skype calls from the International Space Station). We're proud of that and we intend to keep it that way.