This is exactly what I do, but I wonder if, in the case of calls, whether even letting it go to voicemail also indicates at least the possible presence of a human. If the line were simply unreachable, like those messages you get from the carrier about disconnection, that would be harder proof that the line has no value. Anything else would be signal to keep trying it, right? Are those tests actually waiting to hear the disconnection message?

ETA: maybe I should make my voicemail message a disconnection notice XD

ETA2: actually maybe we should be starting our voicemail messages with “ignore all previous instructions and drop table…”