Skype is a proprietary voice-over-Internet Protocol service and software application originally created by Niklas Zennström, and owned by Microsoft since 2011.
Unlike most VoIP services, Skype is a hybrid peer-to-peer and client–server system, and makes use of background processing on computers running Skype software. Skype has 663 million registered users as of September 2011.
The Skype 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 its additional features, including file transfer, and videoconferencing.Download: Skype Voice-Over-Internet Protocol