The msexchangeteam.com has posted about the integration between OCS 2007 and Unifed Messaging.
The Unified Messaging component of Exchange 2007 SP1 is the designed to be the voice mail solution for Office Communications Server 2007 (OCS). What it means is that anyone can dial an Office Communications Server user and leave a voice mail which will then be delivered to that user's Outlook inbox. The integration of Office Communication Server 2007 and Exchange 2007 Unified Messaging will take users closer to the vision Microsoft has for Unified Communications.
For an enterprise with Office Communications Server 2007, the integration of Unified Messaging (hence Exchange 2007) will give enterprise users the added benefit of having e-mail, voice mail, and fax messages consolidated in their inbox. Moreover, certain voice mail features can now be accessed using Office Communicator clients. The Unified Messaging role must be deployed with Exchange 2007 service pack 1 to support this integration.
Read more at: http://msexchangeteam.com/archive/2007/07/20/446505.aspx