[therein]

Haha, that's a nice solution. I recently did something like this and the process really makes you dislike the AT command set. If you don't want to take an old GSM phone apart to find its serial pins, a simple USB GSM modem, pretty much any USB GSM modem should be able to expose a /dev/ttyUSB* interface.

[voltagex_]

Older modems are /dev/ttyUSBx or /dev/ttyACM but newer modems might be using the MBIM [1] standard and don't really expose AT interfaces to the user.

1: https://www.kernel.org/doc/Documentation/networking/cdc_mbim...

[noselasd]

MBIM does however expose an SMS and voice interface - if the device supports it. Though I can't see an obvious way to access it with the kernel API.