Setting up Hosted Exchange, Where to install Unified Messaging?

I am working on setting up a hosted Exchange 2010 environment which will consist of: EdgeServer, Client Access Server/Hub Transport Server, Mail Server, and then our DAG. All of which will be added to/expanded as necessary according to growth. My problem is that I am unsure whether to install the Unified Messaging role on its own dedicated server, or on either the CAS/HT or Mail Server. I know that you are able to do both, but have not been able to find documentation on which would be the most effective, or a particular reason why you would do one over the other. The environment is virtualized so an additional server(s) wouldn't be an issue if it is necessary.

Solution 1:

Microsoft recommends installing Unified Messaging on its own server. This isn't required, but UM can suck up resources pretty well. It also isn't supported in a virtualized setup. This is exactly what they say about virtualizing UM:

All Exchange 2010 server roles, except for the Unified Messaging server role, are supported in a virtualization environment. This is due to the real-time response requirements associated with voice communications with the Unified Messaging server role.

http://technet.microsoft.com/en-us/library/aa996719.aspx