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Skype didn't invent the voice-over Internet Protocol, VoIP, technology but it was the first company to make it easy for the average person to use. Skype also opened up the world of teleconferencing to the masses by offering it cheaply and easily to anyone with a decent Internet connection.

That led to new pricing plans among the phone companies — and ultimately opened the door for new telephony providers, such as Vonage, VG,as well as many cable companies, such as Comcast, CMCSA,(parent of CNBC). It also put a crimp in the business of high-end video conferencing systems, which offered a very similar service for a much higher price.

Skype, acquired by Microsoft, MSFT,last year for $8.5 billion,has more than 660 million registered users.

Photo: Denis Doyle | Bloomberg | Getty Images