What's the history of (bleeping) telemarketing?

When did telemarketing start? And when did it experience its growth spurt?

I can remember the 1960s pretty well, and there wasn’t much apprehension about answering the telephone then. It was almost always somebody someone in your household knew.

By the early 1970s, unsolicited sales calls were still rare, but I do remember getting them. The 700 Club stands out in my memory as being one of the early volume practioners, although I did have a roommate in 1971-72 who made her living as a supervisor of a telemarketing boiler room that hawked whatever they were paid to hawk.

But it wasn’t really a problem until the mid-'80s. Now it’s been almost twenty years that you can expect that most phone calls are a robot wanting a credit card number to promise to pour only the finest Corinthian asphalt in your leaking bathtub.

Are there people who are considered the pioneers?