Also any fast enough accelerometer can be used as a microphone, and no user would complain if an app would ask permissions to use the accelerometer and network

Also any fast enough accelerometer can be used as a microphone, and no user would complain if an app would ask permissions to use the accelerometer and network pretending they're needed for positioning and updates. Not sure though how many phones are using fast enough accelerometers to be used to sample voice. Most should go up to a few hundred Hertz with the right software, but human voice requires at least a few KHz bandwidth.