Microsoft and Skype today announced that they have entered into a definitive agreement under which Microsoft will acquire Skype, the Internet communications company, for $8.5 billion in cash from the investor group led by Silver Lake.

The agreement has been approved by the boards of directors of both Microsoft and Skype.

Skype had 170 million connected users and served over 207 billion minutes of voice and video conversations in 2010. Microsoft has a long-standing focus and investment in real-time communications across its various platforms, including Lync (which saw 30 percent revenue growth in Q3), Outlook, Messenger, Hotmail and Xbox LIVE.

Skype will support Microsoft devices like Xbox and Kinect, Windows Phone and a wide array of Windows devices, and Microsoft will connect Skype users with Lync, Outlook, Xbox Live and other communities. Microsoft added that it would continue to invest in and support Skype clients on non-Microsoft platforms.

"Skype is a phenomenal service that is loved by millions of people around the world," said Microsoft CEO Steve Ballmer. "Together we will create the future of real-time communications so people can easily stay connected to family, friends, clients and colleagues anywhere in the world."

Skype will become a new business division within Microsoft, and Skype CEO Tony Bates will assume the title of president of the Microsoft Skype Division, reporting directly to Ballmer.

Founded in 2003, Skype was acquired by eBay in September 2005, and then acquired by an investment group led by Silver Lake in November 2009.

Other members of the selling investor group led by Silver Lake include eBay International AG, CPP Investment Board, Joltid Limited in partnership with Europlay Capital Advisors; and Andreessen Horowitz.

The acquisition is subject to regulatory approvals and other customary closing conditions. The parties hope to obtain all required regulatory clearances during the course of this calendar year.