SMS is nothing. There are now many Android apps that demand the right to turn on your microphone any time they want to without notifying you. If you carry an Android phone and are not really careful about permissions you are carrying a wire.
I do not remember which apps specifically stated "without notifying the user", however it was worded and I can't find any permission that specifically states that now but I am pretty sure that with MODIFY_AUDIO_SETTINGS permission it can be done by an app using the AudioRecord object:
