That is actually a scam (or can be), where they would play the hang-up sound, play the sound when you dialed the keys and then have a second person continue the

That is actually a scam (or can be), where they would play the hang-up sound, play the sound when you dialed the keys and then have a second person continue the call. It worked because land-lines didn't end the call until both parties hanged-up. That means when you picked up the phone again, you were still connected to them. Don't know if that scam still works, or not, and the same flow is probably used by legitimate senders.