How do robocalls work?

Nearly half of all mobile calls in the United States are robocalls. Here's how robocalls work.

[cadencarlisle]

This should be illegal. I myself receive atleast ten to 20 robocalls per day from EDU Match although my name is on the No Call List, have blocked at least a hundred of their numbers and have made it clear i don't want ANYTHING from them. It's harassment PERIODT. If i myself call someone 10 to 20 times per day after they have told me to leave them alone, i can be charged with harassment or stalking. I don't understand how that same charge doesn't apply to these companies who do it through robocalls.

[blackberrybunny]

That didn't tell me much, sorry. I want to know HOW they do it. How do they use software? How can they dial so many at once? How come sometimes my called ID says something like "SanFran?spam" ?? I read the phone company tries to insert the word 'spam' with the question mark as a way to perhaps indicate the call is a robocall, but I don't know if that is true or not.