VoLTE on the Xperia 10 II - filling in the gaps

General
125

Also on sony Xperia 10 III in Vietnam on Vinaphone network, I can’t active VoLTE and 5G.

126

I’ve heard of it working for people in Australia

First, try this: VoLTE on the Xperia 10 II - filling in the gaps - #112 by koza

Except with this mbn location (given you’re on a X10 iii - if not, see if you have this file):
echo “mcfg_sw/generic/AUNZ/Telstra/Commercial/mcfg_sw.mbn” > modem.conf

If that didn’t work, then maybe try this (given you’re on a X10 iii: https://forum.sailfishos.org/t/volte-and-5g-status/28519?
If you’re not on a X10 iii, you could try get the modem images for your device and do the same approach.