Maybe as secondary from flipper one/zero could be  project with RFID/NFC reader and GSM voice call integration small amount data modem/DTMF over 3,5mm audio  connection to simple.smartphone and software PBX integration.
Maybe at RTU there are some expirience about software free PBX setup/use?

It could be as cornerstone for circular economy project that could work in whole EMEA region. In Africa is verry common GSM implementation in similar services

[[https://www.freepbx.org/|one free PBX sample]]

just with STM board another RFID/NFC project for public services