VoLTE not working with VPN. Help?

[cellulartalk]

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...

More... (https://www.howardforums.com/showthread.php/1925061-VoLTE-not-working-with-VPN-Help?goto=newpost)

Courtesy of WestNet Wireless
www.westnet.ca