Sorry I couldn’t make that headline any shorter! This issue was bugging us for a while, and finally found the answer.
Lync 2010 with Enterprise Voice. User A sets up User B as a Delegate for calls, and sets their phone to forward or simultaneously ring to User B via the Delegates option as per this screenshot:
User B has both a Lync desk phone tethered to their computer via USB, and a headset plugged into their computer. User B answers the call either by clicking on the incoming call toast, or pressing their headset button. Even though their Lync client is set to use the headset as the default device, the desk phone answers the call in speaker mode.
This seems rather weird, especially if you call User B direct they can answer the call straight to their headset. We spent quite some time testing this, trying different options, upgrading firmware, uninstalling/reinstalling anything we could think of until finally I found this technet post: http://social.technet.microsoft.com/Forums/lync/en-US/6e1f9d63-a403-4589-868f-1bd6a1a5e440/lync-delegate-bug?prof=required – scroll down to the last post by William Curley which has this exact problem.
The annoying part is that he claims that Microsoft classify this scenario as a ‘not supported scenario’. The best fix for this is to use Team-Call Group instead of Delegate, but you do lose the ability for Delegates to manage User A’s calls and make meetings on their behalf. This apparently applies to Lync 2013 also, but I don’t have that running to verify.
Lync also won’t like it if you set User A and User B to be delegates for each other, weird things start happening with who’s voicemail the call goes to.
The safest suggestion I have is to just avoid the Delegate option altogether if you use Lync with Enterprise Voice.
I hope this information saves someone a lot of time!
Update 17/10/2013: It looks like Microsoft have released a patch to fix this. http://support.microsoft.com/kb/2889646/en-au has the long title of “PSTN call is routed to an Aries telephone in speaker mode when a delegate answers the call in Lync 2010 by using a USB headset” which fits this exact scenario. It’s a part of the cumulative update for Lync 2010 October 2013 which is available for download, but not in the update catalogue for WSUS servers yet.