This is where you go to get new Communication Client
SDK from Microsoft. Here is a short description:

"...provides a powerful and flexible API for building
client applications for Office Communications Server 2007."

And more:

"The Microsoft Unified Communications Client API SDK
allows application developers to integrate Office
Communications Server 2007 enhanced VoIP, Video,
Instant Messaging, Conferencing, Telephony, Contact
Management and Presence into their applications. "