(FORTUNE Magazine) – The most striking spontaneous mass phenomenon of the past year isn't Howard Dean's out-of-nowhere support or even the baffling rise of Net-powered flash mobs. Overlooked but more important is America's response to the national do-not-call registry. Never mind that two federal courts have blocked the program from being launched as scheduled on Oct. 1. Even a spokesman for the telemarketers says a national do-not-call list is inevitable, and legislators from both parties stepped up to say they'll make sure it happens. The central fact is that before long, some 50 million numbers and counting will be off limits to what is apparently America's most despised industry.

Of course, the industry is playing for sympathy. It claims that if the registry takes effect soon, two million phone solicitation jobs could disappear by Christmas. To which a joyous nation pumps its fist and screams, "Yes!"

We need to appreciate the magnitude of what has happened. America's stampede to zap telemarketers is a true grassroots movement, and a huge one. It shows how extraordinarily deep and intense people's feelings are about this seemingly minor issue. And it tells us something important about the American consumer.

Consider just how unlikely this story is. A major federal rule change affecting thousands of businesses is enacted, though no businesses are lobbying for it, and many powerful businesses are lobbying against it. The change has nothing to do with safety or health, and no scientific studies support or undercut it. In short, this was that rarest of Washington occurrences, a significant action taken for no reason at all except that the people wanted it.

Even more remarkable is what happened next. Within hours of the registry's opening in June, Americans rushed to their phones and computers and put their home numbers on the list (business numbers aren't allowed) at the incredible rate of 158 phone numbers per second. In the first three days we put 13.6 million phone numbers on the registry. Within nine weeks, by the Aug. 31 deadline to be on board for the Oct. 1 prohibition, there were 48 million numbers.

Based on Federal Trade Commission data, we can estimate that this represents more than 40 million people who took action to get telemarketers out of their lives. Let's put that number in perspective. The IRS couldn't even get 1.9 million people to collect their 1999 tax refunds by the April 15, 2003, deadline--free money, but it was too much trouble. After weeks of promotion, about 15 million people watched Whoopi, NBC's new top-rated sitcom, and all they had to do was push a button on the remote. Only 25 million Americans have done any aerobic exercise in the past year--but heck, that's just a matter of life and health. For that matter, only 39 million of us went to a bar or nightclub in the past 12 months.

Bottom line: It's extremely hard to get 40 million Americans to do anything, no matter what inducement you offer. Yet more than 40 million of us, without urging, figured out how to get our phone numbers on the do-not-call registry. The moment the registry became available, we mobbed it.

Federal officials have tried to soften the blow to telemarketers by claiming that the registry does them a service--since people who didn't register have in effect declared themselves willing to listen to telephone pitches. Don't believe it. The consumers who signed up are, on the whole, America's best customers. Well over 60% of the registrations were via the Internet. They are people who value their time, who are busy, stressed, probably have kids, and work too much.

And they're about to snap. That's the large message to take away from our quiet mass uprising. To the 40 million registrants, those dinnertime phone calls are not just irritants. We live with lots of irritants. Those calls are intolerable intrusions into lives already so filled with intrusions and demands that they can't hold any more. That's why so many millions leapt so desperately at a chance to make the phone ring a little less often.

These people are telling us something important, and we'd do well to listen. They're our best customers and most desirable prospects. We need to reach them. But we're on the verge of pushing them too far. In this age of unlimited media and unlimited interconnectedness, marketers still run up against limits. Those limits are human, and if you can't figure out where they are, you're in deep trouble.

GEOFFREY COLVIN, the senior editor at large of FORTUNE, can be reached at gcolvin@fortunemail.com. Watch him on Wall $treet Week With FORTUNE, Friday evenings on PBS.