I've been doing some research on Office Communications Server 2007, and plan on getting this up and running soon. I have been wondering how it will integrate with Exchange UM.
The guys over at the Microsoft Exchange Team Blog have just posted on how OCS 2007 and Exchange UM will integrate to provide voicemail, auto attendant, and subscriber access through OCS.
I will be providing details on my experience integrating the two products with sipX and Asterisk in the future.
If you haven't already subscribed to their blog, do it now. It is one of the most informative blogs at Microsoft, that covers information every Exchange admin needs to know.