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
- Log on to your computer by using administrative credentials.
- Exit Lync if it's running.
- Drag the Lync application to the Trash.
- 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.