Microsoft Office Live Communications Server is an enterprise-grade server that provides the backbone for all real-time communications within Microsoft Office. Presence awareness, IM service, peer-to-peer audio and video, application sharing, and collaboration all depend on it. Microsoft Office Communications Server 2007, the next version of Microsoft Office Live Communications Server 2005, will add on-premise Web conferencing and the ability for Office Communicator 2007 to make and receive voice calls. See more information here… http://www.microsoft.com/uc/default.mspx