If you are planning to install Microsoft Office Communications Server 2007 R2, the unsupported AJAX API impacts the BlackBerry Enterprise Server for Microsoft Exchange for instant messaging implementation against Microsoft Office Communications Server.
Once Microsoft Office Communications Server 2007 R2 is installed, you cannot integrate your instant messaging environment with the BlackBerry Enterprise Server.
The good news is, there is a workaround. Apparently you can first install OCS 2007 R1 on your domain and then upgrade to OCS 2007 R2 leaving a R1 Web Access server installed for the BBIM service to communicate with.
I have not tested any of this yet but will post more updates as I get this going in the lab. Wish me luck.
For more information check out KB17757 on the Blackberry Support site. Since the search on their website is on the top of my list (and not the good list), here's a link. http://www.blackberry.com/btsc/search.do?cmd=displayKC&docType=kc&externalId=KB17757