I’ve been involved in a 12,000 seat, 33,000 user Lync deployment at work over the past few weeks. One of the pain points we had, was publishing free/busy from Exchange for internet connected clients. We use an appliance to give access to our internal resources including OWA and Exchange ActiveSync. And because we are implementing an MDM solution, we are not wanting to make much available externally without having to go through the MDM solution.
Finding good articles covering publishing EWS without exposing everything is few and far between. Luckily I did find a link a couple of weeks back talking about how to do this. For our Lync deployment we are using Threat Management Gateway 2010 (TMG 2010 ) to publish our Lync services to external users. So tacking this feature on is relatively painless. Here is the link here: http://www.confusedamused.com/notebook/publishing-exchange-web-services-remotely-only-for-lync/.