GoKawiilKoppar releases open-source USB-C LTE modem board design on GitHub
A hobbyist project called Koppar has published the full design for a USB-C LTE modem that exposes itself to a computer as a network adapter, serial AT-command ports and a USB sound card, enabling LTE data, SMS and voice calls with audio routed over USB. The repository includes the KiCad schematic and board files, JLCPCB manufacturing and assembly files, a design review document, and RP2040 firmware, letting anyone fabricate and assemble the board themselves.