MS Office Live Communications Server 2005 Enterprise Edition
 

Microsoft Live Communications Server 2005 Enterprise Edition - provides a real-time communication solution that allows you to share presence, instant messaging (IM), and real-time communication capabilities with partners, customers, and suppliers.
Features: Instantly find & communicate with people - Increase individual productivity by using presence, instant messaging, and real-time communication capabilities. Connect people in real time - Collaborate with partners as easily as co-workers, and extend real-time communications to customers and suppliers while you scale to more than 100,000 users. Enterprise-grade, real-time communication solution - Authentication, encryption, and logging ensure information security. Advanced architecture gives you scalability and data recovery capability.

Licenses.
Live Communications Server 2005 Standard Edition Server license with 5 CALs
$1,199 US

Live Communications Server 2005 Enterprise Edition Server license with 25 CALs
This fully packaged product includes one Live Communications Server 2005 Enterprise Edition server license and twenty five CALs (per user or per device).
$4,969 US
http://office.microsoft.com/en-us/FX010908711033.aspx

Microsoft Live Communications Server 2005 requires MS Win Server 2003