Assume that you make a PSTN call by using a Microsoft Lync 2013 for Android client, and that the PSTN number is busy. In this situation, the Lync client plays a ringing tone instead of busy signal. Additionally, you hear the following voice recording:
The number you have dialed cannot take your call right now."
This issue occurs because Lync 2013 for Android does not process the Busy subcode or the "486" message that Unified Communications Web API (UCWA) returns.
To resolve this issue, install the following cumulative update:
2926050 Description of the cumulative update package for Lync 2013 for Android: February 2014