Microsoft has an new update for the client out. It can be downloaded here:https://support.microsoft.com/en-us/kb/3114944
On the March 2016 update there was an issue that phone calls was disconnected after 20-40 seconds. There was also issue with joining the meeting from Lync/Skype client that the user got disconnected all the time.
With this patch, this has now been fixed.
Importent update: Was an old link that has come in here. New link has been added.