In search of a chic cafe hidden in the neon alleys of a teeming Tokyo business district, Hiroki Wai activated the global positioning system on his cell phone and punched in the cafe's phone number. Instantly, a detailed map appeared and a perky female computer voice was navigating Wai toward a hot date with a $9 latte.

"Now turn left; now turn right, walk straight ahead. . . . Hurray, you're here!" the voice chirped from his receiver. A satellite in Earth orbit charted his progress on a full-color street grid displayed on the screen of his cell phone.

"The cell phone is way past being just a phone in Japan," said Wai, 32, a systems engineer who wakes up with his phone alarm at 6:30 a.m. and then uses the phone almost every waking hour to send and receive dozens of e-mails, link remotely to his home-office PC, download music and read newspapers, even novels, during his daily commutes. "For us," he said, "the cell phone is now a way of life."

The cell phone market in the United States is set for a major shake-up after the announcement this week of a $41 billion buyout of AT&T Wireless by Atlanta-based Cingular Wireless, with the merged juggernaut poised to quicken the rollout of such advanced services as access to the mobile Internet and other third-generation, or 3G, technologies. Behind the rush to boost cell phone uses in the United States lies a less flattering truth: In recent years, America has lumbered forward like a John Deere tractor on the mobile information superhighway, while Japan has zoomed ahead like a Z-car.

Technologies considered experimental or novel in the United States have already gone mainstream here, giving rise to an unparalleled cell phone culture. Today, Japan offers a fascinating glimpse into a possible future for Americans: life in a wireless world through the cell phone.

About 70 million Japanese -- 55 percent of the population -- have signed up for Internet access from their cellular phones, a threefold increase from 2000. Cell phones, or keitai in Japanese, are closing in on computers as the device of choice for surfing the Internet. While the Japanese are using their cell phones in the same way many Americans use their laptop computers or personal digital assistants, they also are pulling out their phones to watch TV, navigate labyrinthine city streets with built-in GPS systems, download music, take and transmit home movies, scan bar-coded information, get e-coupons for discounts on food and entertainment, pay bills, play Final Fantasy, even program karaoke machines.

While at least some of these uses are expected to become commonplace in the United States, Japan's penchant for the cutting edge, the cute and the compact has given rise to a particular, occasionally peculiar, keitai culture.

Many young people today even describe their cell phones as extensions of themselves. On subways and trains throughout Japan, keitai addicts, oblivious to the world around them, their hyperactive thumbs furiously typing e-mails on cell phones, have become ubiquitous, even stereotypical sights. One Tokyo TV station recently broadcast a reality show featuring a teenage girl whose cell phone was taken away for one week. She was reduced to tears when she finally got it back.

"I get separation anxiety when I am away from my cell phone. It is part of my identity now," confessed Yoshihisa Amano, 26, who works for a software company in central Tokyo. When he makes or receives a call, Amano creates an identity for himself by projecting an animated character onto the other party's phone screen. Amano controls his alter ego's emotions -- showing sadness, rage or glee -- by pressing different phone keys, and can change characters to suit his mood or caller.

"My keitai is also a video phone, so my callers can actually see me, and I can see them, if we choose," Amano said. He showed a reporter I-chan, a sexy Japanese anime girl in a tight pink sweater and cow-patterned miniskirt who he is now planning to display to friends as his alter ego. "I might not always be looking my best when they call, so I like the characters instead," he said.

On train platforms and highway billboards, cell phone ads dominate the cityscape. The ads underscore the idea that hot new laptops no longer impress the affluent young Japanese; only the latest-model cell phones are turning heads or winning status among peers.

"Cell phones have created extensions of personal space in Japan," said Yuichi Kogure, who teaches a class on keitai culture at Tokyo's Toita Women's College. "You take your world with you when you have your keitai in your hand. In the keitai world, people forget where they are, and women [with cell phones], for instance, can be seen putting on makeup or brushing their hair in the subway, something considered highly rude in Japan in the past. But now, people are walled inside their own little world with their keitai and aren't even aware of what they're doing in public."

In Kyoto, the cell phone culture has generated a new type of university class. Students in more than 52 courses ranging from math to welfare studies at the city's Bukkyo University almost never speak aloud. Rather, they e-mail questions and comments from their cell phones to their professors while in class, and professors answer orally.

"Students can be very shy, and the anonymousness of the system helped them to overcome their shyness," said Kiyoharu Hara, assistant professor of sociology and a mastermind of the university's unusual class communication. "Keitai mail matched the Japanese culture of silently conveying meaning."

Cell phones also have dramatically improved efficiency in marketing. Restaurants advertise immediate discounts on Web sites when they have a slow night, offering price cuts of as much as 15 percent to fill seats with keitai bargain hunters.

But some people complain that so much messaging and surfing with cell phones has resulted in people communicating more, but talking less.

Mutsumi Mukaigawa, 26, an apartment concierge nursing a coffee at Starbucks with one hand, holding her cell phone, decorated with a silver-plated dangling bauble, in the other, has been sending more keitai mails and making fewer calls to her parents, who live four hours north of Tokyo. "My mother just last weekend said my father was sad because I call less and less," she said. "But keitai mail is just so much easier."

Japanese have grown so skilled at writing e-mails on cell phones that many now find it simpler than using computer keyboards. Some have argued that the mobile Internet has taken off in Japan -- as well as nearby South Korea -- because Asian thumbs are smaller and more nimble, and thus more suited to typing on tiny cell phone keys. But the Japanese who launched the service here say size doesn't matter.

Takeshi Natsuno, considered the father of I-mode -- the landmark service of communications giant NTT DoCoMo that granted Japanese easy access to the Internet via cell phones in 1999 -- argues that U.S. cellular phone companies have simply mishandled the concept by employing different signal "standards," or cellular languages, which make it difficult for cell phones to communicate with the Internet.

At the same time, NTT DoCoMo, still the market leader here, encouraged Internet content providers to produce Web sites viewable on cell phone screens by offering them more than 90 percent of the revenue generated from user fees. DoCoMo reaped the benefits as these sites boomed, more subscribers signed up and content providers paid charges for their expanded use of DoCoMo's wireless network.

"Everyone wants to say, 'Oh, the Japanese are strange. They love tiny and miniature things and that's why cell phone services have taken off here,' " Natsuno said. "But the truth is that we are normal, and it's the other guys who are something odd. It's not about being Japanese. It's about knowing what people want and how to sell it the right way."

Special correspondent Akiko Yamamoto contributed to this report.

Young Japanese are avid users of cell phone technology, even to watch television. Last October, a group in Tokyo watched a speech by Prime Minister Junichiro Koizumi. A prototype mobile phone can display images on both sides of the screen, enabling users to take photos, for instance, without opening the unit.