This weekend the most expected version of HMC was released for service providers to deploy it. With this version, service providers can offer OCS (IM, Collaboration, PC-toPC VoIP) services as part of their online services. At the same time support to Windows 2008 and WSS 3.0 SP1 is included in this solution.

You can have access to the bits of the solution from the following location:

http://www.microsoft.com/downloads/details.aspx?FamilyId=C9CBBC69-4AE4-450D-AF5E-F49E7C701CF4&displaylang=en

Or for those who are interested in developing on top of MPS (i.e. self-service portal, namespaces, increase the business logic of the current APIs, etc.) there is a SDK available as well for developers to consume:

http://www.microsoft.com/downloads/details.aspx?FamilyId=CE3FC537-86AE-4802-9A05-43E2A27A4B45&displaylang=en

The documentation to migrate from previous versions is still pending, but it will be released soon. If you have HMC 4.0, you shouldn't expect too much of impact in your APIs or portals already implemented. If what you have is HMC 3.5 or earlier, you should consider a similar migration path like to HMC 4.0 with the addition of migrating LCS to OCS 2007. Don't forget to consider these migrations paths while deploying the solution.