Actually, I think it's been found out recently that thinking that everyone has an "inner voice" is a presumption by those who do. Apparently it's only 25%~ of the population or so that actually have an inner monologue.
It got revitalised again recently resulting in much commotion from people on either side of the fence: shock that someone might never hear their own voice or talk to themselves inside their head, and shock that someone might have this voice talking to themselves, for somebody who has only known silence.
I think there are a couple studies that back it up, but a lot is anecdotal as people describe their side of the fence.
I have an inner voice myself, but I have thoughts and sensations that my inner voice does not voice, and some where it does.
But as far as I know no motor signals are sent to my mouth when I talk to myself (i.e. internal monologue), so this wouldn't read my thoughts. I'm not sure what you're saying.
If you're like most people, you "talk to yourself" internally all the time, so this doesn't seem that far from reading your thoughts.