NEW YORK (CNN/Money) - Tim Girskis recently strolled into Jack's Surf Shop in Huntington Beach, Calif., looking for some Mr. Zog's surfboard wax. He came out ready to buy a new mobile phone from an upstart cell-phone provider called Boost Mobile.

"Sprint PCS charged me for exceeding my minutes, so I switched," Girskis says.

Girskis is every big wireless carrier's dream customer. A 21-year-old car salesman with some money to spend, he's a certified member of Generation Y, one of the only big pools of potential U.S. cell-phone users left.

Unfortunately, a dream is pretty much what people like Girskis remain for most carriers; in the waking world, they've had scant success landing Gen Yers, whose famed skepticism and media oversaturation make them one of the toughest groups marketers have ever wooed.

AT&T, Cingular, Verizon, and others were late to target the youth market, and their scattershot marketing programs and cookie-cutter calling plans left the kids cold.

But now Boost Mobile and fellow youth enthusiast Virgin Mobile USA have begun to crack the code for marketing airtime to Gen Y.

In just California and Nevada, Boost is adding an astounding 40,000 customers a month, almost all of them under 30. Virgin is signing up more than 2,000 mostly young subscribers a day.

How the companies have transformed the ephemeral, intangible, and, let's face it, just plain dull cell-phone minute into a must-have symbol of hip is one of the hottest marketing success stories in business -- and provides some useful clues for growth-starved carriers.

"Boost and Virgin have done a phenomenal job reaching Gen Y," says David Morrison, president of Twentysomething Inc., a youth-marketing consulting firm. "They are just nailing it."

The companies' methods share some basic precepts. For one thing, the handsets themselves aren't the big sell; although some come in funky colors or are co-branded with edgy outfits like women's surf-gear maker Roxy, the phones aren't much different from any others.

But both Boost and Virgin eschew traditional distribution channels, instead focusing on selling in surf shops, record stores, and other places where kids hang out.

Credit checks and binding contracts are out: The average high school or college student has no credit history. The companies rely, therefore, on pay-as-you-go plans. Rather than receive a monthly bill, customers can purchase prepaid chunks of airtime, in increments ranging from $20 to $50, at places like 7-Eleven or Target.

Boost and Virgin are also responding to the same demographic imperative. Thirty years after the invention of the cell phone, two-thirds of U.S. adults own one, and those who don't are expensive to attract.

That's been rough on most carriers, but it has meant opportunity for Howard Handler, Virgin's chief marketing officer.

Formerly head of marketing for the National Football League and MTV (where, among other claims to fame, he helped launch Beavis & Butthead), Handler has spent the last year developing a U.S. cell-phone service aimed solely at people between the ages of 15 and 24.

The teen population alone is about 40 million, and with a whopping $170 billion in annual disposable income, this group is a teeming sea of potential users -- in 2002, just over a third of teens owned a mobile phone. "Everyone is after them," Handler says.

Virgin was first on the case in July 2002, launching its service with a marketing slogan, posted on its Website, attuned to Gen Y's antihype instincts: "Exposing young America to the joy of no bullshit cellular."

Formed by a partnership between Richard Branson's Virgin Group and Sprint, the nation's fourth-largest wireless carrier, each of whom ponied up $150 million, Virgin's U.S. operation was modeled on its earlier push for young users in Europe.

That campaign has been a smash: The European unit recently surpassed 3 million subscribers after less than four years in action, the fastest any British carrier has reached that milestone.

Virgin's U.S. operation leases access on Sprint's network, but it is responsible for everything from customer service and billing to selecting its handsets and marketing its service. Still, by offloading infrastructure concerns, Virgin is able to stick to its forte: developing youth-focused services.

One of its most popular features is its "rescue ring." Virgin users can schedule an incoming call in advance; young adults commonly use it as an excuse to escape from a bad date or a brain-numbing work meeting.

"Not in their wildest dreams would a U.S. carrier have come up with the rescue ring," says Andrew Cole, an analyst with the consultancy Adventis.

Thanks to an exclusive partnership with Handler's old pals at MTV Networks, Virgin also built the Star-MTV platform, which gives users access to music news and the ability to use their phones to vote for videos on shows like MTV's Total Request Live.

The relationship with MTV has helped whet Virgin users' appetites for mobile content. In the past year, users have sent more than 50 million text messages; on average, Virgin's U.S. customers send or receive 25 text messages every month, more than double the industry average.

Those numbers make the rest of the industry salivate: Data services are the holy grail of wireless operators worldwide, who long to rake in the requisite extra fees. But few carriers can currently claim such an active user base.

Boost Mobile takes a more lifestyle-oriented approach to reaching kids. Launched last fall, Boost advertises in print titles such as Surfer Magazine and skateboarding bible Thrasher.

Boost also sponsors Gen Y-friendly events like the Boost Mobile Pro -- the Super Bowl of extreme skateboarding -- held recently at the Las Vegas Hard Rock Casino.

Most Boost subscribers in America likely don't realize that their calls are carried by Nextel, the nation's fifth-largest wireless operator and a company whose brand name, by its own admission, is a total loser with the young.

"Kids see us as the brand their mom or dad uses," says Nextel COO Tom Kelly. Nextel originally set out to target 15- to 25-year-olds itself. But after its market research revealed the brand's weakness, Nextel began to court Boost's 35-year-old founder and CEO, Peter Adderton.

Adderton had launched Boost to go after young users in Australia in 2000 and expanded to New Zealand the next year. He met with Nextel executives in mid-2001; though at first skeptical -- he, like the kids, thought Nextel was a somewhat fusty brand -- Adderton was won over after experimenting with the walkie-talkie feature included in all Nextel phones.

Called Direct Connect, it's one of the industry's few easily differentiated services. In May 2002, Nextel bought 66 percent of Boost for an undisclosed amount.

"I never expected to do a deal with Nextel," Adderton says. "But I knew kids would love Direct Connect."

Now more than 35 percent of the minutes used by Boost customers go toward the $1-a-day unlimited-use walkie-talkie feature. The company has also forged relationships with companies like surf-gear makers Quiksilver and Billabong to develop products that reflect Boost's youth focus.

As the result of one such partnership, Boost appeals to 15- to 20-year-old women by offering phones bearing the Roxy brand, a sister to the Quiksilver line. These developments have helped bring Boost's total U.S. subscribers to 140,000 in little more than a year, even though the service is still available only in California and Nevada. (Nextel is expected to decide whether to roll it out in other states by December.)

The initial youth market inroads by Boost and Virgin represent the industry's first concerted forays into niche demographics, but certainly not the last. Branding airtime is a new concept, but it has obvious applications to other demographics and special-interest groups.

Companies like MTV and Disney have already shown interest in running their own specialized services, possibly aimed at sports fans or entertainment buffs. If carriers can crack Tim Girskis and his fellow Gen Yers, going after other niches ought to be a much easier call.