Established phone companies see Skype as an ominous cloud, with its 200 million active users who spend more than 300 billion minutes yearly on Skype calls. Skype intends to continue its role in helping to crumble established telephony business models, with plans to double the number of developers at the center.

Karlheinz Wurm has been the director of the development center since April 2011, but he's not new to Skype. He spent five years at the development center in Tallinn, Estonia. He's so full of energy that he's almost boiling over, and he's excited to have a view of Stockholm's waters from his office in the old brewery. Besides the most recent work on the Windows Phone version of Skype, the development center was home to versions for the iPad, Android and iOS.

Being available on all platforms is basic to the Skype business model, unlike, for instance, Apple's FaceTime video-calling application, which works only with iOS.

"That's like having a notion of only talking to people whose shoes are a certain color. You're wearing black shoes. Then I won't talk to you," he says.

Skype became a division of Microsoft after the software maker acquired it last year. Skype CEO Tony Bates, who previously worked for Cisco, is based in Palo Alto, California, and reports directly to Steve Ballmer. Microsoft made a gigantic investment in Skype -- not only with the acquisition price of US$8.5 billion, but also investments in further development. Also, the acquisition opened doors for Skype to Microsoft's product development.