I have been sutding up on UCM 6.X and I was under the impression from Cisco at one point UCM 6.X was going to have a Windows version and a Appliance version.
All the documentation I am reading make me think it is Linux only.
I have lots of customers for one reasong or another that want to stay on MS.
You are correct here. We have been meeting with Cisco recently and it has been confirmed to us on more than one occasion the UCM 6.X will be Linux only :(
I have also heard that the 7.X train may have a Windows version (can't be confirmed).
Hope this helps clear things up!