This issue occurs when you click the call me option to join a meeting as an anonymous user from Microsoft Lync Web App. When this issue occurs, the call is dropped immediately or disconnects after you try to answer it.
Resolution
To resolve this issue, install the July 2015 cumulative update 5.0.8308.920 for Microsoft Lync Server 2013 web components server.
Cause
This issue occurs because the public switched telephone network (PSTN) dial-out is initiated from Unified Communications Web API (UCWA) instead of from Audio Video Multipoint Conferencing Unit (AVMCU) in Lync Web App.
