Now before anyone has a heart-attack due to the title pay special attention to the fact that ‘R2’ is strategically left out. The full UM integration is still fine for Office Communications Server 2007 R2 and Lync Server 2010, only the original (aka R1) release of OCS is impacted.
This statement is confirmed by the Supported Deployments table shown in the Release Notes for Exchange Server 2010 SP1.
Upgrades to the UM platform in the SP1 release of Exchange Server 2010 has changed the way things work with Unified Messaging and have done so in a way that could prevent some calls which originate from Exchange UM (like Play on Phone or the Auto Attendant) to possibly not be routed correctly to OCS endpoints.
So basically the impact here is that any organizations running Exchange Server 2010 and OCS 2007 with Unified Messaging integration should investigate this in detail before applying Service Pack 1 to Exchange. Preferably the OCS deployment should be upgraded first, but as this is a larger undertaking (no in-place upgrade path) it may not be ideal.
Realistically I do wonder how many organizations are running the latest version of Exchange Server yet have not updated from OCS 2007? I’m sure there may be some but I have not seen a pre-R2 OCs deployment in the wild for some time as the added features in R2 (e.g. 64-bit architecture, desktop sharing, dial-in conferencing) were a huge benefit to upgrading. But the reality is the Communications Server team has been 110% focused on delivering the Lync product for some time now and I’d guess that during development of Exchange Service Pack 1 the teams decided that the updates offered more benefits than retaining compatibility with a much older version of OCS.