The UCMA API is up on the public downloads site!  The UCMA library is used to write SIP servers for broadcast IM, query response bots, etc. used managed code (C# or VB.NET). 

This is the API that I used in my UNC340 session at TechEd.  I'll post the slides and code from that session later today.

Check it out!

http://www.microsoft.com/downloads/details.aspx?FamilyID=1aaf0e4f-804c-4888-9c7c-81d7f7a6ddef&DisplayLang=en