Currently, we have unified messaging 4.21 with exchange 2003.
Soon we will upgrade to unified messaging to 5 or 7 to compatible with exchange 2007.
However, our unified is running on windows 2003, but exchange 2007 will run on windows 2008.
It might be a stupid question, but I want to make sure that: is it ok unified runs on windows 2003 and exchange 2007 runs on windows 2008??
Its more of a microsoft issue, not Unity per say. Unity's only requirements is that it either works with Exchange 2007 on 2003 or Exchange 2007 on Windows 2008. Both are supported in the CCO Documents.