RequireWIFIForIPAudio in mobility policy isn't applied for Skype for Business iOS and Android devices

In Microsoft Skype for Business Server 2015, you use the following cmdlet to set the Skype for Business iOS and Android devices only to be able to make audio calls by using Wi-Fi:

Set-CsMobilityPolicy -Identity "Identity" -RequireWIFIForIPAudio $true

However, the devices still are able to make audio calls by using the standard cellular phone network.

To fix this issue, install the following updates:

• The July 2018 cumulative update 6.0.9319.534 for Skype for Business Server 2015 and Unified Communications Managed API 5.0 Runtime.
• The July 2018 cumulative update 6.0.9319.534 for Skype for Business Server 2015, Web Components Server.
• The July 2018 cumulative update 6.0.9319.534 for Skype for Business Server 2015, Front End Server and Edge Server.