Actually all phones have to work this way, because the radio communication is essentially a shared medium (spatial beamforming notwithstanding). Hopefully modern protocols are properly designed to use encryption and nonce identifiers such that the other phones only see opaque packets. But a reprogrammed baseband could easily disrupt communications for everyone on the same cell, and there's no way around that. This is a major source of the culture of locked down secrecy that ends up pervading the rest of the stack.