I have a single multi-role install of Exchange 2007 for 600+ users that I have had no issues with. My thoughts are to install Exchange 2010 on two servers creating a single DAG group, hardware load balance (some Barracuda HLBs) for HUB & CAS roles on the two servers, and also implement the Unified Messaging role on the two servers. I have not played with the UM role and need some insight on if this makes good sense implementing it this way... on two already multi-role servers instead of separating that role on it's own hardware. I probably will only have 200 UM users for the first year or two before I would bring in the remaining 400+ users, and I know I can add additional servers to spread the load if need be in the future. I only have money enough for the two servers this coming year though and don't want to set myself up for problems.

Hi , Yes you can install it with other roles also I want to share that I M using since last one year with MB, CAS and HT roles and there is no issue I also have 100 + users on it. Regards. Shafaquat Ali.M.C.I.T.P Exchange 2007/2010, M.C.I.T.P Windows Server 2008, M.C.T.S OCS Server 2007 R2

Agree with Shafaquat. More resources below may help during the UM planning: The “Planning Your UM Deployment” section in Planning Roadmap for New Deployments Understanding Unified Messaging Performance and Scalability The Three UC Amigos : Exchange 2010 Unified Messaging TechNet Webcast: Exchange 2010 Voice Mail enabled by Unified Messaging (Level 300)James Luo TechNet Subscriber Support (http://technet.microsoft.com/en-us/subscriptions/ms788697.aspx) If you have any feedback on our support, please contact tngfb@microsoft.com