I stumbled over this on Google -
What's New in Exchange Server 2007 SP1 Beta 2 Extensibility
Ch-ch-changes! They are a comin'. Microsoft Exchange Server 2007 Service Pack 1 (SP1) Beta 2 includes some changes that affect developers, including updates to transport extensibility and additions to Exchange Web Services. To help you prepare to develop for Exchange Server 2007 SP1, this article provides a brief overview of these changes.
Furthermore the UM / OCS part of SP1 is available publicly now -
Requirements for Exchange Unified Messaging integration
If you want to deploy Communications Server 2007 in order to use the Exchange UM voice capabilities and in order to integrate with the Exchange UM service, you have to install the Exchange UM role to Microsoft Exchange Server 2007 Service Pack 1 (SP1) Beta 2. Based on the SP1 release notes, Exchange 2007 SP1 Beta 2 introduces the following features that are required to integrate Communications Server 2007 with the Exchange UM service...
And of course there are the original Microsoft Exchange Server 2007 SP1 Release Notes that eventually will be updated for Beta 2