Microsoft has developed a Skype-style free Internet voice service for mobile phones that analysts believe could wipe billions off the market value of operators such as Vodafone. The service is included in a mobile version of Microsoft Office Communicator due to be released this year. It will take the form of a VOIP (voice-over internet protocol) application that allows Office users to make free voice calls over Wi-Fi enabled phones running Windows Mobile software. It uses the Internet as a virtual phone network as well as accessing email, PowerPoint, and other Office applications.