Consider the following scenario:
You configure an announcement service to transfer incoming calls to unassigned numbers to a predetermined destination in a Microsoft Lync Server 2013 environment.
You call an unassigned number from Microsoft Skype for Business for iOS device.
In this scenario, the call is disconnected upon answering instead of being transferred to the predefined destination.
Note If the call is from a PSTN number, Microsoft Skype for Business for Android, Microsoft Skype for Business for Windows, or Microsoft Skype for Business desktop client, the call can be transferred successfully.
This issue occurs because the announcement service does not hold the first media call before blind transferring it.
To fix this issue, install the April 2016 cumulative update 5.0.8308.956 for the Lync Server 2013, Response Group Service.