If you're looking for additional context, it would likely be found by reading the previous post which I linked in the post body. Here is the link again: https://lemmy.zip/post/53113975
Edit: But, that’s besides the point! Give the SPIRIT phone project a look on github! https://github.com/SPIRIT-org/SPIRIT
To be slightly more accurate, I wrote "I continued to mess around with a mobile broadband modem, and got it working! With a caveat… it only works when plugged into wall power.", "it" referring to the mobile broadband modem. Only the usb connected broadband modem requires "wall" power to function, technically it only requires 25W consistently to be provided to the pi5, or some other direct power.
The device is a great little handheld that functions as a full linux computer that works completely on battery power! I bet your landline can't do that!
But, that's besides the point! Give the SPIRIT phone project a look on github! https://github.com/SPIRIT-org/SPIRIT