When she whipped out her iPhone, Erica Sadum could feel her husband's eyes roll. But she had a point to prove. In less than a minute, she was able to report to the skeptics around the dinner table that Menno Simons, whose followers are known as Mennonites, was in fact born in 1496.

Apple Inc.'s iPhone, which went on sale nine months ago, isn't the only so-called smart phone that provides itinerant access to the Web. But its wide screen and top-quality browser make it easy to use and read, which means it can in seconds change a lighthearted conversation into the Pursuit of Truth.

"It's turned me from a really annoying know-it-all into an incredibly annoying know-it-all, with the Internet to back me up," said Sadum, a technology writer in Denver. "It's not a social advantage."

New technology always brings new habits with it, some of them unpopular. The mobile handset took phone calls into the streets, and the BlackBerry created a generation of thumb-typing e-mail addicts. Some smart phones hook their owners up to facts and figures that ordinary people pull off the Internet with a proper computer.

As University of Southern California student and iPhoner Cliff Smith put it, "I have the ability to clear up any confusion."

Fewer than 1 percent of the 219 million cell phones in the United States are iPhones, according to M:Metrics. (One possible reason: An iPhone costs about $400.) That hasn't been enough to trigger a broader boom of Internet browsing on hand-held gadgets. The percentage of U.S. mobile phone users surfing the Internet over the past year has stayed flat at 13 percent, M:Metrics found.

Internet companies, though, report that they have been getting more traffic from mobile devices, much of it from outside the United States. And the companies have noticed that iPhoners use their handsets differently from other owners of mobile phones. They search the Internet more, particularly for movies, restaurants and news, according to market researchers, and they watch more videos on YouTube and do more online banking.

THE NEXT BIG THING?

Google Inc., Yahoo Inc. and Microsoft Corp. are betting that mobile services and advertising will be the next big business opportunity. For example, the Yahoo Go service for Internet-connected cell phones (not yet available for the iPhone) showcases a program called PriceCheck. It allows people to check prices at a number of stores by entering a product's bar code number.

"Maybe you will remember to do price comparisons for flat-screen TVs online before you head out the door to a store like Best Buy, but maybe not," said Steve Boom, a Yahoo senior vice president. "Your need for that kind of information is immediate."

Wil Shipley, a Seattle software developer, uses his iPhone at the Whole Foods fish counter to check Web sites for updates on which seafood is the most environmentally correct to purchase. He quizzes the staff on where and how a fish was caught. Because he carries the Internet with him, "I can be super-picky," he said.

The clerks who work the fish counter don't mind. "He's confirming on the Internet things that I am saying," said Whole Foods' Ken Shugarts.

That's nice, but as Sadum warned, you should pick your iPhone moments carefully. "The second you go into the pocket for the iPhone, you have disconnected yourself from the conversation," she said. "No one has the patience."

Nora Wells certainly doesn't. When she's with iPhone-toting friends and a question comes up, she braces herself, as she did recently when it was suggested that they go out for beers "stat." Inevitably, someone wanted the exact definition.

"The iPhone even gave us the Latin," said Wells, a radio traffic reporter who learned that stat is an abbreviation of statim, "immediately," often used in the medical field. "We probably could have been having our beer in the amount of time it took to look it up."

The proud owner of a Motorola Razr cell phone (from which she can forward text messages — something she happily noted was beyond the iPhone's capabilities), Wells worries that iPhoneism might overtake even her.

"I feel so pressured to get one," said the 27-year-old resident of Venice, Calif. "People expect it from me. It's the hip, young, fun thing to do."

Or not.