A. You should talk to your Microsoft support representative for the most recent information, because the situation is evolving.
The fundamental issue here is the quality of the service. Remote Desktop has had bi-directional audio support since Remote Desktop Protocol (RDP) 7. (RDP 7 was introduced with Windows 7 and Windows Server 2008 R2, but the Remote Desktop Connection client has been updated for Windows Vista SP1 and Windows XP SP3 to add RDP 7 support.) The problem isn't the bi-directional audio, it's making sure the Lync or OCS client has the correct information about the network to optimize the experience.
When you run the Lync or OCS client on your local machine, the client can analyze the server and its connection to it. It can then optimize audio quality and other factors based on the available network, ensuring you get the best experience for your connection. Now imagine you run the Lync client on a Server 2008 R2 Remote Desktop Server Session Host or Windows 7 virtual machine in the datacenter and connect remotely to that OS using RDP from a remote location. The Lync client will analyze the connection to the server (which would likely be in the same datacenter) and see a great network connection with no latency, so it will be configured for that setup. However, you're actually sitting at a different location with a very different network, so the quality of your voice and video will suffer.
You can still use the IM, presence, and Web conferencing features of Lync with RDP and be supported, but not the audio and video features. The official support statement is available on Microsoft's site .