It doesn't even need to be something that Grandma can use. It just needs to be something that will let you pass the various "you must have a smartphone to participate in society" checks. But considering banks and the like won't even let you use AOSP in many cases, I sincerely doubt one can get a Debian phone to work.

i hear the bank argument a lot and although i can understand the importance for those without another device, i'm a little stunned people rely on modern pocket spyware to monitor their accounts. maybe i know too much, or too little, but my banking concerns are infrequent and always in a browser.

Welcome to Poland, where you can't transfer more than ~$13K daily without using mobile auth (bank app). Currently only the PKO bank implements this (and I hope this backfires on them), but I'd not be surprised if others follow.