Show HN: A USB-C LTE modem that gives my computer a phone line

A developer has created Koppar, a USB-C LTE modem that gives computers their own phone line, enabling LTE data, SMS, and voice calls with audio transmitted over USB. The device requires only a nano-SIM card and one USB-C cable, appearing to the computer as three standard devices: a network adapter, serial ports for AT commands, and a USB sound card for call audio. The open-source hardware design, built on a 4-layer board with the Quectel EC25-EUX module, includes full documentation, KiCad files, and manufacturing specifications for others to build their own units.