Calls use GSM not VoLTE with German carriers - potentially big problem?

ell1e · July 10, 2026, 6:11am

Hi, I help postmarketOS users test the ClockworkPi uConsole. They noticed that during calls with the firmware as-is (no firmware updates from the point the device shipped from ClockworkPi to the user) the modem will drop to GSM for calls rather than use VoLTE when using German carriers, checked via `mmcli -m 0` during the call.

At the same time, Germany is apparently planning to phase out GSM calls soon, I think in around one and a half years. This seems to mean calls will soon be unavailable unless this is fixed.

Therefore, I wanted to report this since there seems to be a problem with the modem, and at the same time ask if there are any official instructions on how to fix this. If there aren’t yet, there probably should be some.

white-round-square · July 10, 2026, 7:58am

there is a firmware update, not sure what it does though

github.com/clockworkpi/uConsole

wiki/How-to-upgrade-4G-extension-firmware.md

master

# Precautions
The following-mentioned flashing operation requires your familiarity with Linux and firmware flashing.   
**Please do not attempt to try it without sufficient experience!**  
**Please do not attempt to try it without sufficient experience!**  
**Please do not attempt to try it without sufficient experience!**  

as we will not be held responsible for any consequences. Thank you for your understanding.

once you flashed the new firmware, if you need to downgrade,check [this](https://github.com/clockworkpi/uConsole/wiki/How-to-downgrade-4G-extension-firmware) out.  

Therefore, there are risks involved in flashing the 4g ext, and it is necessary for you to have a certain understanding of these background information. During the testing process, it is also not possible for me to test whether all SIM cards worldwide can easily connect to the internet through **usb0**.

# Purpose

A more convenient way to use 4G ext on the uConsole,no setup, no nmcli ,just insert 4G card and power on 4G ext, that's it

# Power On 4G ext

we assume that you already know how to power on the 4G ext by https://github.com/clockworkpi/uConsole/wiki/How-to-use-the-4G-extension

This file has been truncated. show original

ell1e · July 11, 2026, 8:44am

The 4G internet reportedly no longer works after the upgrade. Seems like the cdc-wdm0 gets replaced by a ttyUSB2 device in the nmcli listing, and attempting to bring it up results in this:

# nmcli device up ttyUSB2
Error: Connection activation failed: PPP service failed to start.

This seems to happen despite mmcli -m 0 showing a registered state with access tech “lte”.

ell1e · July 11, 2026, 3:53pm

I think this could be why. So is the new firmware only compatible with rndis? Since that seems to mean that it may no longer work on any newer Linux device in the future and it’s a dead end. But so is non-VoLTE 2G calling that appears to currently be used by the modem for e.g. “O2 Germany”.

So the situation looks concerning, as far as I can tell. I wonder whether ClockworkPi is aware of this development? But perhaps I’m missing something.

white-round-square · July 11, 2026, 7:43pm

you are digging deep!

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Calls use GSM not VoLTE with German carriers - potentially big problem?

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