I think there should always be physical off-switches for microphones: it should be possible to know that the thing is not listening. But smartphones also have other private information on them than what can be captured by its microphone.

I don't think the smartphone is inescapable at all, and I don't think any of the conveniences it offers is worth surrendering one's privacy. But there is a tendency in businesses to ignore the fact that some potential customers do not have smartphones. I wonder if legislation against this might be possible.