There are huge differences between OCS 2007 R2 Server and Lync 2010 Server of course. The client of the communicator server changed also, so Microsoft Office Communicator 2007 changed to Lync 2010. Although connecting to OCS 2007 R2 via Lync 2010 not allowed, with a little trick, we can do that.
Be careful, only the OCS 2007 R2 features availabe on the Lync 2010!
We need to add a registry key on the user machine under the HKCU \Software\Policies\Microsoft\Communicator, named DisableServerCheck DWORD, and add as 1 as value.
Here is my exported key, you can copy-paste to a .REG file to simply import it.
Windows Registry Editor Version 5.00
That’s all folks.