I keep getting calls from "Unknown Caller" and there's nobody on the other end of the line. I don't understand what the scam(?) is.
eta: I stay on the line in case it's a computer that needs time to kick in. I check my bill for suspicious charges. Nothing.
It's a telemarketing center, most likely. It's time-consuming to have actual people dial all the phone numbers, so they have a computer do it. Then once someone picks up, the call is transferred to a live person. If nobody is home, the call center doesn't have to waste their employees' time on the call. (No comment on wasting everyone else's time . . .)
Anyway, they use statistics to judge what % of computer-dialed calls will get answered by humans, so they always are dialing more phones than there are people to talk to customers. Sometimes the algorithms end being wrong, and the computers get more people on the phone than there are employees to pick up the calls. When that happens, the computer hangs up on you - hence the strange ghost calls.