Natacha Vilson was catching up with an old friend she had bumped into on a New York street recently when, without even saying "excuse me," the friend seemed to be talking into space. Because he was using a tiny wireless headset perched on one ear that was barely visible, she didn't realize at first that he had taken a call on his cellphone and was no longer talking to her.

Ms. Vilson, a college student, was put off and finally said: "I'm talking to you, will you please take that off?"

Such mix-ups are happening increasingly as the small, robotic-looking phone headsets that perch in the wearer's ear become the latest high-tech accessory of choice.

Using a technology called Bluetooth, the devices generally are 3 or 4 inches long, weigh less than an ounce, and don't need to be physically plugged into a cellphone, freeing users from dangling cords and making it easy to keep the little pod clipped onto one ear constantly, even at home. They can connect with a phone that is as far away as 30 feet, though most users still keep their phones in a pocket, purse or belt clip.

"It is like my third earlobe," says Raj Mohammed, a technology project manager at a New York mutual-fund company.

While many users find them convenient and fun, the new headsets can create peculiar social situations. As was the case with Ms. Vilson and her friend, bystanders are often unaware that a user is wearing one. Indeed, users of Bluetooth headsets often appear to be talking to themselves.

Another pitfall: "Half the time people think you're talking to them when you're really not," says William Robbins, a doctor in Orlando, Fla. He was in a supermarket recently enjoying a bit of risque banter with an ex-girlfriend over his headset when the woman next to him thought he was talking to her.

Although exact sales figures are not available, wireless-equipment makers and phone operators alike say that sales of the headsets have increased sharply in the past year, fueled by new technology that makes them easier to use and a jump in the number of moderately priced phones equipped to work with them.

For example, roughly a quarter of all phones sold in the U.S. will be Bluetooth-ready by next year, up from just 3 percent last year, according to Yankee Group, a Boston-based consulting firm. Analysts expect sales of Bluetooth headsets will continue to grow in the next few years.

At the nation's biggest wireless company, Cingular Wireless, which is co-owned by BellSouth and SBC Communications Inc., Tim Towster, senior director for accessories, says wireless-headset sales have grown very rapidly in recent months. Cingular expects "a huge spike" in sales of the headsets around the holidays, Mr. Towster says.

Most Bluetooth headsets cost between $50 and $150, and users say most sound good and are easy to wear -- though complaints about them picking up noise from the wind outdoors are common. They run on various batteries that last from a low of 2.5 hours to more than 15 hours of talk -- longer than most cellphones -- assuming users remember to charge them. Leading manufacturers include Motorola Inc., Plantronics Inc., the Jabra division of GN Store Nord AS, and SonyEricsson, a joint venture of Sony Corp. of Japan and Sweden's Telefon AB L.M. Ericsson.

The wireless-headset craze is part tech-geek, part fashion, as Motorola and Oakley Inc. underscored recently when they introduced a sleek $295 pair of Oakley sunglasses with a tiny Bluetooth headset attached to the temple.

But wireless headsets can make for etiquette problems. When Reginald Davis, a pharmaceutical-sales manager in Washington, bought a wireless headset in November, his wife, Shan, thought it looked cool -- until he started wearing it constantly, even at family gatherings, where Ms. Davis's sister-in-law would ask her: "How can you stand it?"

For months, Mr. Davis says he had assumed his wife could tell from the lights on the earpiece whether he was on the phone, but Ms. Davis hadn't noticed them. Unable to predict whether he would ignore her or respond, she got in the habit of forging ahead with whatever she needed to say. "I just keep going," she says. "I know he can hear me. He just doesn't answer me."

"The headset has become such a part or my everyday life that I didn't recognize how much it is actually in my ear," says Mr. Davis.

Not everyone thinks the headsets look cool. "You look like a half-assimilated Borg," says Roger Entner, an analyst at Boston consulting firm Ovum, who nevertheless occasionally dons one; he likens carrying on an in-person conversation while wearing a headset to "shaking hands with gloves on."

Headset-using customers particularly annoy Noga Oppenheim, a waitress in Manhattan's Greenwich Village. One of them, she says, expected her to read his lips as he silently mouthed "cappuccino" without interrupting his conversation. She says people using the headsets often wave her off with a dismissive gesture. "I don't like it at all," says Ms. Oppenheimer. "It makes me feel like I'm bothering them."

But for some people, wireless headsets can solve social problems. When Nathaniel Feldman, a doctor from Short Hills, N.J., had to talk on his cellphone about complicated medical situations during his commute into Manhattan, fellow passengers would sometimes ask him to keep quiet. That hasn't happened since he got a wireless headset in June. "People must think I am talking to the person next to me," he says.

Similarly, the maitre d' at Bayard's, a restaurant near Wall Street in New York says he gets far fewer complaints from nearby diners when callers discreetly use wireless headsets than when they talk into regular phones.

Like them or hate them, wireless headsets seem here to stay -- until new technological advancements render them passe. Even Ms. Vilson, the college student put off by her friend's headset chat, recently bought Motorola's trendy RAZR phone and a Bluetooth headset. "I have to be up to date with the trend," says Ms. Vilson, who adds that her friends wouldn't be seen outside their dorm rooms with an outdated phone.

Even though there's no need, Ms. Vilson says she sometimes keeps her phone in her hand while using her headset just to offset the impression that she's insane or rude. "I have it in my hand so people can see that I'm on the phone," she says.