You may or may not be aware but with Lync Federation to MSN enabled and a remote contact using MSN 2011 you can now do audio calls – this could be a useful feature if you have users on MAC’s as I believe they have to use the MSN client (I haven’t tested this however).
To get this working you need to change the default encryption type for Lync from ‘RequireEncryption’ to ‘SupportEncryption’. If you don’t change the encryption type you will receive an error: ‘there was an encryption mismatch between you and xxxx’.
Here is how you do it:
set-csmediaconfiguration -encryption supportencryption
All should now work.