The complaints about telemarketing I've mainly received are from people, particularly on do-not-call lists, who are woken up, pulled out of the shower, away from meals or other conversations, or had other activities interrupted by unwanted phone calls. These are people who never, ever, EVER buy anything from cold calls. They liken telemarketing to people being paid to accost them in the street.
Some of them don't have answering machines and voice mail. Some of them are anticipating important calls. None of them appreciate having their chain yanked.
Like it or not, the phone - especially the home phone - is seen as a very personal space. Physical mailboxes aren't so much, because it's trivial to rapidly shuffle flyers and ads into the bin while checking the mail. Even so, it's an unnecessary inconvenience, and can escalate to unpleasant levels - see
http://www.macobserver.com/article/2002/12/06.11.shtml for an example.
There's a market for "No Junk Mail" stickers and plaques. There's a market for spam blockers for email and advertising blockers for web browsers and proxies. There's a market for administrative/secretarial services which go through your business mail and toss out the junk mail.
There are "No Soliciting" signs. There are Do-Not-Call lists. There are even phonecall-blocking devices already on the market, although they are relatively useless against telemarketing en masse.
The new devices would be bought by people who would otherwise be a waste of a telemarketing call anyway, because they hate telemarketers and cold calls and would never buy anything from them. This way, the buyers are freed from having to be subjected to telemarketing, and the telemarketers aren't able to connect to people who hate them. Such a situation might even be seen as a win-win for all concerned.
Still, I appreciate the feedback.