This is one step away from building the bitcoin phone
Some of the thinking behind SATSLINK device. We will be writing the lower level and some of the application, but this will be more intended as bring-your-own-app. More info on specs here https://satslink.com/specs and
venn 
new keypad 
Discussion
Which, since cheap 1TB microSDs, is technically possible already yesterday.
I’d drop apple in a heartbeat for a bitcoin phone with an open source App Store
What defines 'Bitcoin phone'?
I would say a phone that is both open source hardware and open source software, who’s software is made with bitcoin integrations in mind. Built in keys on a secure element, Lightning wallet, etc.
This is my dream, but basically it’s a phone whose primary functions are call, text, and interfacing with the bitcoin protocol.