This is just a coincidence thrown in for humor.
In a wargame group I’m in, Princess “Trixie” is the head of state for a fictional country called Saxe Burlap, maybe I should introduce her to Prince VoLTE of the Empire of Ikea? Then ZoLTE can “start to work” on Trixie with his charming attitude.
It looks like bm818-tool needs to be run as root (with xhost + command to give display permission) since chat command is in /usr/sbin which is not in the PATH for normal user.
When running bm818-tool as root, I get the same output, but I can’t make calls when in 4G (I have to manually switch to 2G only) and incoming calls automatically switch to 2.5G.
What does CBS means in bm818-tool ? I could not find anything related searching online.
Also the incoming call is coming as greyed out (I can hear it ring), but if I lock the screen and press power button, I can see the option to take call in lock screen.
For the record, it isn’t useful unless you know what and why you’re doing.
If you can’t make calls, you can’t get the same output during a call.
You will find half a dozen mentions in this forum though. However amarok and dos covered it. Best to ignore CBS completely for now, particularly as it isn’t relevant to VoLTE.
Did you reboot your phone after successfully running the bm818-tool? I believe that that is effectively a requirement.
Power cycling the modem is enough 
I should have been clearer, this is the output when phosh shows 4G. During outgoing call (after switching to 2G), it showed EDGE instead of LTE and during incoming call it showed GPRS. So VoLTE is not active. I have it ticked in bm818-tool and I did reboot / power cycle multiple times.
Now we need to find a way to launch it as root from home screen bm818-tool volte check does not work on mobian trixie (#9) · Issues · Librem5 / bm818-tools · GitLab
I figured how to launch it from terminal with pkexec, but adding this to .desktop did not work.
The latest version of bm818-tool does it already.
It is active, but there’s apparently some incompatibility with your career that prevents IMS calls from working. You want to either keep it disabled, or somehow debug it over QCDM.
Today I swapped sims between Librem 5 and FLX1, so Librem 5 got Vi and FLX1 got BSNL. VoLTE is working on both phones (bm818-volte-check now shows LTE during the call and on FLX1 gnome calls shows the call is VoLTE enabled). I’d be happy to share any specific logs (I’m not familiar with these components to debug it myself).