Let me announce that the GSM-to-Telegram bridging automation initiative just reached another milestone. Voice calls from Telegram back to GSM network do work now.
The project is designed on top of the Nix build expressions, so users don’t need to do any particular installation besides installing the Nix package manager, getting the right GSM USB dongle, filling in configuration settings and running the main ./run.sh script.
The main problem of this milestone was as follows: It is not possible/I don’t know how to read the desired GSM extension number from Telegram. I wrote a simple ARI application which starts the Telegram part of a call and waits in chat for the extension number. When the user types it in, the application established the GSM part of the call.