Your 3G dumbphone is not as dumb as you think. Considering the threat models from that era, it's most likely more manageable remotely and less compartmentalised

Your 3G dumbphone is not as dumb as you think. Considering the threat models from that era, it's most likely more manageable remotely and less compartmentalised. Btw, you could acquire a Mobile-ID SIM that will work on a rooted phone (but also with feature phones, if you wish).