got a sales call not sure i pick up and no one answers

These idiots call every day; sometimes 2-4 times a day. They do not leave a message on my machine, and when I pick up they don't answer or say anything. Could someone tell me exactly what their point is?

Personally I believe it's telemarketers just generating calls. Some MUST make a number of calls per day. Whether they get an answer or not, they are still counted as making a call. That's how they get paid. Irritating little crooks.