- Verify that you have deployed / upgraded the Client Access, Mailbox, and Hub Transport servers in your organization to Exchange Server 2010
- Install the Exchange 2010 Unified Messaging server role and add Exchange 2010 UM servers to the Exchange 2003 UM dial plan
- Configure all IP gateways or IP PBXs to send incoming calls to the Exchange 2010 UM servers.
- Install the Unified Messaging language packs you need on the UM servers in your organization.
Almost same Question / Answer, I provided, please look here: Transition to Exchange 2010.