Microsoft Lync Server 2010 is the new name of Microsoft Office Communicator Server and it now delivers complete presence, instant messaging, conferencing and enterprise voice capabilities through a single, easy-to-use interface that is consistent across PC, browser, and mobile device. Administrators benefit from a single, consistent management infrastructure, new capabilities to increase availability, and interoperability with existing systems.
Microsoft Lync Server 2010 ushers in a new connected user experience transforming every communication into an interaction that is more collaborative, engaging, and accessible from anywhere. For IT, the benefits are equally powerful, with a highly secure and reliable system that works with existing tools and systems for easier management, lower cost of ownership, smoother deployment and migration, and greater choice and flexibility.
Refer to http://www.microsoft.com/en-us/lync/default.aspx for more information.