Hello,
I would like some advertisement for the FreeCalypso development board: https://www.gofundme.com/fcdev3b-board-production-2umevjw
Michaela is maybe a "bad hacker", and uses illegal methods and non-free software. But there is now a working open source GSM stack. Making voice calls and sending SMS-es is working on some hardware with open source firmware without blobs. Controlled using AT-commands. https://www.freecalypso.org/
People who want to make FOSS firmware can learn from the code. Creating a GSM stack without examples is very much work. The source code, documentation and the design files for the hardware are published.
There is only 4500 USD needed for the production of 20 fully assembled boards, 25% is funded at the moment. Anonymous funding is possible so far I know.
With regards, Paul van der Vlis.