If Google and it's outsourced partner can listen to the recordings, 3 lettered agencies can too. Even if they currently can't, they'll soon make a law to grant them access to Google's and Amazon's. After this, a hijacking, explosion, or terrorist attack would occur. They would argue that it could have been prevented if place X had a listening device installed. And that's all it would take to push a law mandating the…
The good thing about trying this is people would definitely notice the increased bandwidth usage of their phone streaming audio in real time, all the time.