300 million Americans, 10 digits 0-9. Even dialing totally blind you'd expect a ~3% hit rate. Limit that to actual area codes (public information) and bias it t

300 million Americans, 10 digits 0-9. Even dialing totally blind you'd expect a ~3% hit rate. Limit that to actual area codes (public information) and bias it towards the more populous ones, and you could probably do considerably better. I'm not sure how important lists are.