Easier to just use a usb/minipcie modem and operate directly from the 'server' - no batteries, no OS to crash, no nothing, simple AT commands on linux "middleware" (modemmanager etc.)

I remember having an old Nokia phone that would expose the AT command set over a USB tty, yet still be useful as a handset. This feature wasn’t advertised in the box, I found it accidentally. Would love to find a low cost phone like this again.