Symptoms
Assume that you set up your Announcement service in Microsoft Skype for Business Server 2015 to transfer calls. When a caller calls an unassigned number by using the Skype for Business iOS client from a device such as an iPhone, the call transfer fails.
Resolution
To fix this issue, install the June 2016 cumulative update 6.0.9319.259for Skype for Business Server 2015, Response Group Service.