Software buttons can't be trusted. Smartphone manufacturers need to put hard switches on the power, cellphone transceiver, wifi, bluetooth, camera, mic and speaker. Also, all the major components should be replaceable, especially batteries.
The case for replaceable batteries can be made from a convenience/durability/sustainability point of view, sure, but how do replaceable batteries improve trust?
Not a directly trust related issue, but an often conflated factor. (assuming you dont do something exceptionally silly like make the batteries have a serial interface and protocol that can be its own attack vector. Wait a sec...)