But romping with the boys didn't mean Perry shed her signature glam for grunge. "I didn't wear the same outfit twice," she says. "I know how much people follow the visual aspect and they want to see eye candy. I used Freddie Mercury as my model—he was a serious artist and musician who never lost sight of the fact that you also need a good look."

After wrapping the Warped tour, Perry headed overseas. In London, she played summer shows at the 200-capacity Water Rats and the 1,000-capacity Scala. "Girl" and "Hot N Cold" were both No. 1 singles on Billboard's European Hot 100. In the United Kingdom, "Girl" was the No. 4 best-selling single of 2008. U.K. sales now stand at 495,000 for "Girl" and 328,000 for "Hot," according to the Official Charts Co. And, much as in the States, the single sales have outstripped that of the album. "One of the Boys" peaked at No. 10 on Billboard's European Top 100 Albums chart. In the United Kingdom, it has sold 279,000 copies, according to the OCC.

Perry launched her first headlining tour Jan. 23 at the Showbox in Seattle, with a brief detour to perform at the Grammy Awards as part of the My Grammy Moment promotion where a fan performed alongside her during the telecast. The tour will hit theaters with 1,000- to 2,000-seat capacities; there will be an 11-date European run, including several U.K. performances, and stops in Japan.

"Our philosophy has always been to sell places out," says Creative Artists Agency's Mitch Rose, who worked Perry's tour. "We set the ticket price at $18-$20 for most markets, because we wanted to ensure a sellout. We could have charged more and we know we're leaving money on the table, but making sure the rooms were packed was our first priority."

But just because the rooms are small doesn't mean Perry will keep her show simple. "I have the guy who creates stages for Madonna working on this tour," she says. "I'm indulging my obsession with fruit and cats and designing all different outfits."

This quirkiness is leading her to other opportunities—Perry also says she'd like to develop a clothing line at some point, but she's in no hurry. "It would take two years to do it right," she says. "I don't want to do something rushed and sloppy. I look at something like Gwen Stefani's line, L.A.M.B., and that took forever to do."

Stefani is a role model of Perry's, not just for her sense of style but her long career. Perry believes interacting with her fans is key; she's constantly blogging and responding to MySpace messages, as well as putting in time after every show to chat and sign autographs.

"All the big pop girls come across as being so scared and so distant," Perry says. "I understand diva-ness, but I cultivate an image as the pop star next door. You need to have some mystery and some privacy, and there are parts of me that I hold back. But at the same time, I love meeting people and e-mailing with them and blogging about funny things." Perry's MySpace page has been viewed 28.3 million times and also provides a phone number users can call to hear updates.

"The fact that she's making so many connections with fans now is good, because they'll be more loyal," Cobb says. "She loves to tour, and we're planning on sending her through markets multiple times. We want to make sure she has the right kind of growth and keep working this record as long as possible."

As for Perry, she's focused on using everything she learned in the past to build her career. "There are times I want to call up the old labels and say, 'Now who's laughing?' " she says. "But then again, if I hadn't had all those obstacles, I don't think I'd be as smart about the business as I am now." ••••

Additional reporting by Mark Sutherland in London.