If you’re not a tween/teenage girl or don’t live in proximity to one, you may not yet be in on the phenomenon created by 20-year-old Kevin, 18-year-old Joe and 15-year-old Nick.

They opened for Miley Cyrus on her fall “Hannah Montana” tour to the delight of shrieking girls everywhere. Their song, “S.O.S.,” catapulted to No. 1 on iTunes. Their second album has sold more than 900,000 copies. And that’s just the beginning.

Earlier this month, the band became the youngest act to sign a deal with concert presenter Live Nation. The multimillion dollar, two-year pact includes promoting 140 shows in theaters and arenas worldwide by the New Jersey-based brothers starting Jan. 31 in Arizona.

“We know where we’re going to be at the end of 2009,” says Joe, incredulously.

While some may consider putting such big money behind a still-developing act risky, many in the industry believe it’s actually a very shrewd move.

Indeed, the band’s three February shows at the Gibson Amphitheater in Universal City, Calif., set a record for the fastest sellouts in the venue’s 35-year history when the first two shows sold out in two minutes.

Even the brothers admit they can’t wrap their heads around the Live Nation deal. “In a weird way, it’s humbling,” Nick says. “People think you’d get a big head about it, but it’s like, ‘Wow. Someone would do this?'”

All this success comes after the band got off to a rocky start. Its debut album came out on Columbia in 2006 to little fanfare because their primary champion, Columbia president Steve Greenberg, had departed the label by the time it was released. The band soon parted ways with Columbia and signed with its current home, Hollywood Records. (The album, It’s About Time, is now a collector’s item with an asking price of up to $299 on Amazon.com)

The comparisons with Hanson are inevitable: like Hanson, these three brothers write their own songs and play their own instruments, giving them more credibility than the average boy band. (The Jonas Brothers even name check Hanson in their song “That’s Just the Way We Roll.”) While their songs are solid power pop, the tunes possess more of a rock edge than those by many of their contemporaries.

The tour is the first step toward global domination that Hollywood Records parent, The Walt Disney Co., has provided in the past for such acts as Hilary Duff, Cyrus and the cast of “High School Musical,” all of whom have enjoyed platinum and/or multiplatinum success. Though mainstream radio has been largely resistant to these acts, there are signs that the Jonas Brothers will break through with new single “When You Look Me in the Eyes,” which is already receiving airplay on pop stations in New York and Los Angeles.

“The only way to get onto pop radio is to make records with broad appeal. They have begun to do that,” Greenberg says. “This is different from being big in Disney’s proprietary media, where super-serving the core young audience is all that matters.”

Not that the Disney juggernaut will stop any time soon. In mid-June comes “Camp Rock,” a Disney Channel movie which the network hopes will be the next “High School Musical.” The next month, the band is due to release its third album: Joe says the topics are “girls, missing a girl on the road or liking someone or having fun on tour.” Musically, Nick adds, “it’s got more Elvis Costello-, Prince-type influences.”

The Disney assault continues with the brothers’ own TV show, the taping of which has been temporarily thwarted by the writer’s strike but is likely to start in the fall. The series revolves around the boys as spies, whose cover is they are also in a struggling rock group.

“It’s about (being) a high school student who can’t make your five o’clock job because you have band rehearsal and you have to save the world,” Joe says.

But first comes the tour. From the Cyrus outing, they learned how to captivate a large audience, but their lessons weren’t confined to the stage. When tickets for their tour went on sale, they decided that the first 20 rows would only be sold at the box office of the venue through a lottery system and not online.

“What happened on the last tour was so difficult,” says Kevin, referring to the issues surrounding the red-hot Cyrus tour, including tickets selling for more than $2,000 by scalpers and through sites like eBay.

“We wanted our real fans to be right up front so we can play and have the energy from them rather than having some really rich cats sit(ting) down,” Joe says.

Life on tour is good for the trio, with one minor complaint: “We drive all night to get to where we’re going, so we have to get out of our bus and into the hotel room,” Kevin says. “Sometimes people are outside your hotel at 4 a.m. and you just woke up and you’re a little discombobulated, but we still try to have as much fun as we should.”

However, there is a cap on some kinds of fun. All three brothers wear purity rings, a symbol that they will remain pure until marriage. “Before we were even in a band, it was something we did,” Kevin says. “Now, of course, everything we do is under scrutiny and under the spotlight, especially being part of the Disney environment.”

They’ve learned to live under the intrusive glare of that spotlight where even standing near a female under 50 can result in a tabloid love match.

“Jo Jo’s always been a great friend of ours,” says Kevin of the 17-year-old singer. “(She’s) walking through the snow, she had high heels on and Joe helped her. A couple of pictures (later) and now they’re dating and they have a nickname already.”

Even Nick isn’t immune. He’s been romantically linked to Cyrus, although he has maintained they are just friends. “It’s hilarious to me that people think so much about my … relationship,” he says. “It’s really weird, but it’s cool.”