To reiterate, I'm not suggesting it should be able to listen in on conversations, but rather that it may plausibly be able to detect recurring environmental vibrations. For example, let's say your phone is left on a table unnattended, then if your house is near a train then it may be able to sense the regularity of the train's passing (whose schedule itself varies throughout the day, providing a unique fingerprint for both determining which train it might be and your position along that train's route).

Yes, for sure you can sample and detect lower frequency vibrations. That's the whole point of an accelerometer :)