VoLTE not working with VPN. Help?

[Oakesia]

We have some iPhones supervised with MDM which use an always on VPN that cannot be disabled. It seems that VoLTE doesn't work right with this setup. When trying to make a call the phone hangs for like 20 seconds after which point it'll either die saying 'call failed', pretend to connect but there's no audio, or eventually connect properly.

Does anyone know what we can modify to allow VoLTE through properly? There's nothing obvious in the logs.

[TwitchyPuppy]

Either they allow the use of VoLTE within MDM (if there’s such a thing) or turn VoLTE off.


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