Pssst! Here’s the 411 on, well, 411.

In the past few weeks, thrifty New Yorkers have latched on to a new service that provides free directory assistance, which, considering Americans spend about $8 billion a year on such calls, could prove to be quite a boon.

The Boston-based company Jingle Networks rolled out 1-800-FREE-411 nationwide in September, but until last month it had largely gone under the radar for most city dialers. Now, the 917 area code, reserved for Manhattan cell phones, has shot up to no. 2 on the list of most frequent callers of the number, just behind Los Angeles.

The company does no advertising except for a single billboard in Philadelphia, relying instead on word of mouth.

In exchange for the free number, callers are subjected to a 10-second advertisement targeted to their request. For example, if calling for Grimaldi’s Pizza in Brooklyn Heights, the caller will first hear a woman’s voice promoting a special at Domino’s for “three medium one-topping pizzas for just $5 each.” The caller can then be connected free of charge to the advertised business or ask for the original number.

Not all business numbers set off ads: A request for the phone number of Score’s, an upscale Manhattan strip club, did not prompt any counteroffers.

The service is the brainchild of Scott Kliger, a 37-year-old entrepreneur from Michigan. “Like every other entrepreneur, I looked at the success of Google and said, ‘What have they done right and what remains to be done?'” Mr. Kliger, the co-founder and CEO of Jingle Networks, said in phone interview last week.

The company has raised $5 million in venture capital. Mr. Kliger’s philosophy is that consumers should not have to pay to find the phone number of a company with whom they want to do business. In this model, it’s the business instead that pays.

About 6% of callers take the number of the business being promoted rather than the one they demanded.

While Mr. Kliger declined to say exactly how many calls the company has received, he put the number in the “hundreds of thousands.”

Every year, Americans place about 6.6 billion calls to information – including about 2.1 billion calls from cellular phones. Across the country, prices range from 25 cents to $3.49 a call.

Kathleen Pierz, managing partner of the Pierz Group, a directory assistance consulting firm in Michigan, estimated that New Yorkers place about 300 million calls a year for a total cost of about $450 million. “For a consumer, directory assistance is like underarm deodorant,” Ms. Pierz said. “It’s there and you need it and nobody thinks about it until something goes wrong. This might finally get people to think more about directory assistance.”

Free Internet search engines have already taken a large bite out of the industry’s profits, she said. The free service may have telephone companies worried, but a Verizon spokesman, Jim Smith, said he believes people will stick with the old-fashioned system.

About 3 million directory assistance calls are placed to Verizon each day for $1.25 a call. “The chances of a resounding success are mitigated by our belief that people want numbers accurately and quickly,” Mr. Smith said. “If they have to sit and listen to an ad, their frustration level will probably go up.”