I did it manually forever ago with some terminal commands, but I believe they made a GUI to turn it on now, assuming you have the bm818 modem.
To install it, go to the terminal and use:
sudo apt install bm818-tools
Should put an icon on there for you. May have to reboot for it to find all the information properly. I installed it recently to view the firmware version of my modem, and it definitely took a reboot before it figured itself out. There’s a checkbox for turning on VoLTE. Mine was checked when it found the modem already, but I think that checking it is supposed to toggle it for you. If not, we have to dig up that old batch of commands.
I think they are these alarm messages your government might send when need be.
You might have to update your modem firmware for the tool to work properly. I did this after contacting support. There is at least one thread about this.
I’m curious for your success on Mint Mobile, are you using a SIM card that Mint Mobile provided?
The main reason to “fiddle” with the firmware now from what I understand is to get the phone to wakeup from suspend mode (battery saver) when a call comes in. That’s actually what I’m in the process of doing right now.
I am also a Mint Mobile customer (on my Samsung Note 9 daily driver). I have another Mint Mobile SIM card that I bought for my Librem 5. But I haven’t activated it yet. Would it be better to run the bm-818 tools program before, or after activating the SIM card?