Running Office 14.4.9 updates and many before that.  If you activate or deactivate an iMessage account using the built-in Messages application, Lync can no longer make or receive calls.  Calls received will automatically go to voicemail.  Outbound calls just ring and ring.  The phone setting in Lync were all three set to Lync as well.

The only way I've found them to work is to following the first instructions at the following link:

https://support.microsoft.com/en-us/kb/kbview/2691870?wa=wsignin1.0

1. Log on to your computer by using administrative credentials.
2. Exit Lync if it's running.
3. Drag the Lync application to the Trash.
4. To remove your existing Lync preferences, delete the following files:
   • Users/username/Library/Preferences/com.microsoft.Lync.plist
   • Users/username/Library/Preferences/ByHost/MicrosoftLyncRegistrationDB.xxxx.plist
   • Users/username/Library/Logs/Microsoft-Lync-x.log

If you activate or deactivate an iMessage account steps 1-4 must be performed, otherwise, phone calls fail.  One additional annoyance I've noticed is that Lync tends to hand with a red X on the icon in the dock when this happens as well.  You must use the terminal and do 'pkill Lync' in order to close it.

Hi MSGuest,

Can you install the latest update and then check again ?

https://www.microsoft.com/en-us/download/details.aspx?id=36517

Best regards,

Eric

That may have fixed it.  I'll continue to monitor it, but I couldn't reproduce it trying some variations I did in the past. I'll post up if it stops working again.  It took me months to finally figure out that the Messages app and deleting the preferences was key to getting it working.

Thanks!

The problem returned.  Not sure if it had anything to do with installing MS Office 2016 Preview, but that's about the only thing that I've changed.  Seems the be the exact same behavior as before.