I can't help to do this on UT, but I can explain what you are looking for.

Sometime there is two operators in a SIM card : your local operator and a roaming sponsor.
As example in europe, roaming sponsor is often Orange or BICS (Belgacom).

So if you are in another country, the SIM card must act like it is from the roaming sponsor.
It can detect and switch context automatically, or you need to switch manually.
To switch manually, you have to run a "javacard applet" on the SIM card, to do that phones have a menu like "SIM-Toolkit-App".

@alagirialagiri no idea, I was just listing Halium11+ devices hoping it will help to maybe have VoLTE oneday.

For VoLTE it seems best to wait some month for a clear view.

So in order to have a more recent device than my old E4.5, I'll go with a classic Pixel 3a, even if its halium version is older.

Hello,

I've an Aquaris E4.5 (16.04) and I'm looking for the next phone to continue the UT adventure.
In my country, VoLTE is an important topic because 2G/3G will be shutdown.

I understand that OTA-8 VoLTE support is limited to some VollaPhone, but for those who want to buy a new phone now and hope VoLTE support in futur, I tried to read topics about VoLTE, and if I sum it up :

• Qualcomm and Mediatek will be supported
• Halium11 seems to be the minimum

Based on devices database, Halium11+ devices list is short as today :
"Niche" phones : Fairphone4, Volla22/Quintus/X23, F(x)tec Pro1 X
Sold widely : Xiaomi Redmi (Note) 9

If your telco don't accept all VoLTE compatibles phones, but only thoses they tested, it seems Xiaomi Redmi (note) 9 is the only choice ?

Thank you