Skype is a proprietary voice-over-Internet Protocol service and software application originally created by Niklas Zennström and Janus Friis in 2003, and owned by Microsoft since 2011.

The service allows users to communicate with peers by voice, video, and instant messaging over the Internet. Phone calls may be placed to recipients on the traditional telephone networks. Calls to other users within the Skype service are free of charge, while calls to landline telephones and mobile phones are charged via a debit-based user account system. Skype has also become popular for its additional features, including file transfer, and videoconferencing. Competitors include SIP and H.323-based services, such as Empathy, Linphone, Ekiga as well as the Google Talk service.

Skype has 663 million registered users as of September 2011. The network is operated by Microsoft, which has its Skype division headquarters in Luxembourg. Most of the development team and 44% of the overall employees of the division are situated in the offices of Tallinn and Tartu, Estonia.

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