> SoC exist with builtin LTE/CDMA/etc.

But inside the Echo? It's not my area of expertise, but I'm almost certain that there are people with the expertise that are looking for exactly that and if Google or Amazon had those built in, we'd know about it. I think we can at least rule that one out.

As for the compression, that is very interesting indeed. I had no idea you could compress voice that much. If / When they're going for 24/7 recording, this would be most likely the way to go and it would be extremely hard, if not impossible, to detect.