The last time my friend Evan got his hair cut, a few weeks ago, he could barely keep his eyes on the mirror. Instead, he was mesmerized by what was happening the next chair over. A young woman kept yanking her customer's hair too hard while braiding it into cornrows -- because, all the while, she was gabbing and trying to balance her cell phone on one shoulder.

"He sucked his teeth at first, then grimaced a few times," says Evan. "Finally, I think the retort he lobbed at her was, 'You need to get off the phone. I'm tender-headed!' "

In a world where, everyday and to no one's surprise, zoned-out iPod wearers unconsciously block the center aisle on the Metro, cell-using cabbies barely acknowledge backseat passengers and business execs lunch "together" while clicking away at their BlackBerrys, it might seem as if there are no frontiers left to cross in the digitizing of America.

But you'd be surprised. There's a not-so-subtle shift going on, a migration beyond the cars, buses, subways and streets. A few examples:

Amazing Scene One: A businessman e-mailing from a table isn't even worth a second glance these days. But how about a businessman spotted, as one recently was, typing on his BlackBerry while using a public urinal? That's good for hours of water cooler conversation.

Amazing Scene Two: This past Wednesday, a man was fatally stabbed in front of a New York restaurant. A witness who saw the blood-soaked victim lying on the sidewalk was quoted as saying, "People were just walking by with their iPod headphones on. That was tripping me out, that they kept on walking."

Amazing Scene Three: A colleague recounted watching a bakery clerk struggle with a malfunctioning cash register and ask for help from a co-worker at the same counter -- unsuccessfully, it turned out, because the second woman was chatting away on her cell. "It's $8," the cell-phone user yelled before going back to yakking. Unfortunately, that wasn't the question that had been asked. The first cashier shrugged her shoulders apologetically and said, "She doesn't like it when I interrupt her call."

It's one thing to tut-tut about these situations. But the fact is, all of us who own a cell phone, PDA or digital music player swore we'd never use it in certain ways -- and sooner or later, we've caught ourselves doing just that. Think: Have you ever shushed someone to answer your cell? Or worse, just ignored them? Or maybe you've slowed down the deli line because, listening blissfully to "Thriller" on your iPod, you didn't realize that the person behind the counter was, yes, talking to you. As one technophile wrote me, we all think, "I'm one of the good guys!! [But] it happens to the best of us."

Why are we drawn into behavior we thought we'd never condone? Many people would say it's simple -- it's just plain rudeness, the self-centeredness that grows from living in a me-me-me world where your music, your friends and your work can all travel around with you all the time.

I disagree (which isn't the same as condoning it, I hasten to add).

Yes, every time you interrupt "real life" to attend to a device, you're short-changing a relationship -- but you're also feeding one, with the person on the other side of that electronic impulse. Cell phone and PDA users are constantly balancing the rights and expectations of those in their "real" reality with the rights and expectations of their virtual relationships -- a relatively new situation for humankind. With this double community now a 24-hour-a-day thing, we're still trying to figure out how to deal with it politely. And we don't always get it right.

To really take in what a change this has been in American society, think back to the introduction of the Sony Walkman, in 1979. It's been said that this moment marked a human paradigm shift -- it was the first time people could carry their private worlds with them everywhere, no sharing. Sony co-founder Akio Morita understood this and was so nervous about it that he insisted that the device carry two earphone jacks, so people could listen together. He thought it would be "rude for one person to be listening to his music in isolation," he later wrote in his autobiography.

Of course, as we now know, most Walkman users opted for solitary use -- and loved it. But the dynamic that critics then grumbled about -- people off in their own little worlds, even while in public -- remains unresolved. In fact, it's become harder to navigate after, with cells and PDAs, those "little worlds" became social spheres.

All of this means much more negotiating -- and misunderstanding. Take my friend Jennifer and her husband Bryan. They've agreed that, whenever he whips out his BlackBerry during what's supposed to be their private time, she can fine him $5. The rule, she says, was instilled a few months ago, when he started e-mailing someone at work during the middle of one of their conversations. It's come up often since. Eight months pregnant, she found one occasion, at the obstetrician's office, particularly galling.

"I was gushing emotionally about our healthy little baby inside" when he took out his BlackBerry, she told me.

Bryan is nothing like Inconsiderate Cell Phone Man, the Cingular ad campaign character known for using his cell during a trial, a support group meeting, even his own wedding. (Though, judging by the character's popularity, there are many ICPMs out there. He's grown into a hit, even making the "Today" show last week.)

But where Jennifer sees his e-mailing as abandonment of the real (her) for the virtual, Bryan sees it as being present for both, "the same thing as reading a magazine" -- which is what Jennifer was doing. Plus, he adds: "If it's work hours, I need to be connected to work."

It turns out that Bryan is dealing with some serious social pressures to communicate -- and not just with Jennifer. In 2000, a survey by the management consulting and technology services company Accenture found that, of American workers who had taken at least a week-long vacation that year, 83 percent said they had brought mobile technology along. Of those who used it to keep in contact with the office, more than half began the interaction themselves. (All these numbers would surely be higher now, since the post-PDA craze.)

When HR, the magazine of the Society for Human Resource Management (SHRM), explored why anyone would do such a thing, one of the answers that came back was: out of consideration for other workers. With many companies running whippet-thin, people are more conscious than ever that, while they're away, someone else has to do their job. The vacationers want to help out. And they're often expected to. As one tech geek tells me, "The boss knows I have access to e-mail all the time, I'm gonna look like a slacker if I'm not taking a peek at least every now and then, even during my off-hours."

(For those wondering, the number of respondents who admitted to checking in for questionable emotional reasons was small: Only 7 percent said they'd done it because "it felt good to be needed.")

E-mailing-while-traveling is also part of another American obsession: multi-tasking. Which brings us back to people in the services industry who are talking on the phone, while ignoring you.

Imagine this: You serve streams of people every day. And, increasingly every day, the customers ignore you, because they're on their cell phones. So you buy one and use it at work because -- well, they're on the phone, aren't they?

It happened to cab drivers. First, riders stopped "seeing" them by deciding the backseat could be used as a private phone booth; then, so ignored, the drivers got on the horn themselves, removing anything but the barest function of getting riders from Point A to Point B.

Now imagine all the people who deal with distracted customers every day, finding themselves asking questions several times because the customer is on the cell or wearing those little white iPod buds. We've all seen pictures of power brokers on the phone while getting a manicure or a haircut. Why not me? the stylist must think. And white-collar workers aren't any better behaved: In a survey last year, SHRM found that more than 40 percent of HR professionals contacted randomly said that they had a policy regulating cell phone use on the job. Another 12 percent said they planned to have a policy in place within six months.

Baltimore caterer Nancy Sachs tells an interesting story. "I used to ask my people to turn off their cell phones before we did a job," she says. "Now I just confiscate them. A lot of my guys are in the back, out of sight of the clients, so they don't understand why it matters if they're on the cell or not."

In a multi-tasking society, waiting for something to happen, or even doing a single job -- taking inventory, for example -- is the kind of activity that, when someone asks us what's we're up to, makes us respond, "Nothing." So if we're not doing anything, why not get on the phone?

The same logic could be applied to iPod use. For years, some companies have allowed office-bound employees to play music in their cubicles as long as it's not too loud. The key was not to intrude on other people's space. So isn't wearing an iPod earpiece, which is completely private, actually being a better cubicle-mate? A friend goes a step further -- he likes to take his iPod on a crowded Metro, he says, as "a more polite way to ignore people."

He expands: "To stand there face to face with no reading materials in hand and still have nothing to say to someone, not even a hello, that's plain rude where I come from. But, hey, I'm wearing headphones. I'm actually doing something."

Of course, there is a price to be paid. Researchers have long said that the quality of our human interactions, even small ones, can make a big difference in our moods and ultimately our health. And clearly, a distracted employee is less likely to be proactive at work, or even to notice when something is going wrong.

In answer to this dilemma, many people vow they're going to turn off their cell phones or BlackBerrys and put away their iPods. I say, don't. What's needed is practice, not avoidance. In the early days of computers, offices found themselves dealing with oodles of wasted hours as employees surfed porn sites, gambled, played games or just goofed off. But computers were here to stay, so the companies studied the problem and set standards of allowable and non-allowable use. Over time, wasteful computing time has greatly declined.

We need to do the same thing with these little worlds we carry around. One main hint: If, like the man getting his cornrows done, you feel the other person's digital connection is getting in the way, say so. Many people don't -- again, trying to be polite. But politic censure is the only way societal rules get written. And you'd be surprised at the difference it makes.

Last week, rushing to the office, I had a long chat with my cabbie. "Thank you for sharing that story with me," he said. "It makes me feel good." It was the best thing that happened all day, and when my phone rang -- the boss -- the etiquette to follow was clear.

I didn't answer.

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Sandy Fernandez is a Post editor and recovering BlackBerry abuser.