Software wallets are convenient to use but potentially insecure and difficult to move to a new device; hardware wallets, while secure and portable, are cumbersome and often difficult to use.
The SIM card seems like a perfect solution: a piece of secure hardware controlled by the user that is always in the phone and can be moved between devices.
Like metamask through the SIM card, a SIMask
Android has built-in APIs:
These have been used to create a proof of concept APP used in the demo video linked below