This NY Times article explains how millions of people are paying to avoid telemarketers. I was doing it myself -- paying about $8/month to block all callers who refuse to identify themselves. It was very effective. I'd only get maybe one telemarketer call per month. It works because the telemarketers hate to identify themselves. They usually want to lead you to believe that some reputable company is calling.
There are also gadgets like TeleZapper that work as well.
As the article explains, it is annoying to pay $8/month to the phone company to solve a problem that the phone company has created. Why can't the phone company have its own opt-in system?
Actually, avoiding telemarketers is not the main reason I had the service. I really got it to identify callers. I have no interest in taking calls from people who refuse to identify themselves. I can see why businesses might take anonymous calls, but why would individuals? I cannot think of a single time in which I wanted to take a call from an anonymous caller.
To identify callers, you need 3 things: Caller ID service from Ma Bell, a caller id phone or display, and a service or box to reject anonymous calls. The anonymous call rejection is needed because millions of Americans block their caller id, and many of them don't even realize it. With the fancier anonymous call rejection services, the caller has a chance to unblock or identify himself on the fly. Otherwise, the caller has to hang up, dial *82 to unblock caller id, and redial the number.
So why don't I have it anymore? I dropped Ma Bell, and switched to MCI for local and long distance service. It just has simple anonymous call rejection. It works ok so far, but it is too early to tell. Occasionally, an anonymous call slips thru. I'll probably get some complaints from people who have to dial *82, but why are they calling anonymously? I have yet to hear a good reason for anonymous calls (to private homes).