You can't blame promoter/producer Arthur Fogel for wondering just how gargantuan U2's Vertigo tour could have been if the band simply kept on playing. After all, not one ticket went unsold for the 131

You can't blame promoter/producer Arthur Fogel for wondering just how gargantuan U2's Vertigo tour could have been if the band simply kept on playing. After all, not one ticket went unsold for the 131 shows on the trek, which began March 28, 2005, in San Diego and wrapped Dec. 9 in front of 47,000 fans at Honolulu's Aloha Stadium.

Having been on the road in fits and starts since March 2005, U2 was clearly in a celebratory mood in Hawaii, as Bono danced onstage with a woman from the crowd during "Mysterious Ways" and even pulled a lucky guy out of the audience to play piano with the band during "Who's Gonna Ride Your Wild Horses." Whether waving the American flag high above his head amid opener "City of Blinding Lights" or writhing on the stage blindfolded for "Bullet the Blue Sky," the frontman was holding nothing back.

The evening reached an emotional climax during "One," when Bono encouraged the audience to hold their cell phones aloft and light up the venue "like a Christmas tree." Fans were also asked to send a text message of support to the One campaign to end world poverty, with some names of participants in the audience chosen to be listed on the backdrop.

When all was said and done, Vertigo clocked in as the second-highest grossing tour of all time: $389 million from an astonishing audience of 4,619,021, second only to the Rolling Stones' concurrent A Bigger Bang trek, which may continue into 2007, and has grossed more.

"I sometimes try and visualize, what would be the universe?" Fogel muses to Billboard. "In other words, what if you could just play and play and play? We sold over four-and-a-half million tickets on this tour, but we still underplayed basically everywhere we've gone."

Vertigo visited arenas in North America through late May 2005, then played stadiums in Europe throughout that summer. In the fall, it was back to North America for a run that included six shows at Toronto's Air Canada Centre and six at New York's Madison Square Garden.

February and March took U2 to South America, which was originally to be followed by dates in Australia, New Zealand and Japan. Those shows, however, were postponed until the fall due to a serious illness that struck within the immediate family of a band member. Details have never been publicly disclosed.

Getting Vertigo back on track was the final hurdle for Fogel, who has been associated with U2 in a promoter capacity since 1981 but has produced the band's last three world tours via his TNA organization. He and U2 manager Paul McGuinness admit they're always thinking about the tour in one way or another, even a year before the first fan has filed into a venue.

"We're in contact all the time," McGuinness tells Billboard of Fogel. "As the record develops, the production develops. And depending on when the record is finished, we have an imaginary start date. That's subject to change, but the thinking about the production is always simultaneous with the making of the album."

The Vertigo stage set was designed by Willie Williams and was marked by an ellipse-shaped extension that allowed band members to travel far into the general-admission crowd on the floor. It required 30 semi trucks to get from place to place, according to stage manager Rocko Reedy. On a good day, it took two-and-a-half hours to assemble, but that duration could nearly double depending on weather and venue configurations. After being loaded post-show onto the trucks, the stage was packed onto three 747s to travel to the next venue.

Early in the tour, U2 performed in front of seven see-through LED curtains, onto which images and patterns were projected. Later, a giant, super high-tech LED screen was used instead to form the backdrop.

"All the stuff we use is always serial number 001," Reedy says proudly. "The first time they create this type of technology, it's U2 that uses it. Then everybody else under the sun goes out and gets it, so we just have to come up with something new."

That said, Vertigo has not been without its share of drama. The tour got off to a rocky start after a disastrous presale for paid members of u2.com in January 2005, when demand far exceeded the ticket allotment, prompting shut-out fans to blast management and even band members themselves on Internet forums.

"The demand was artificially stimulated because, quite honestly, a lot of ticket scalpers had joined u2.com planning to trade the tickets," McGuinness says. "It was clear very early those tickets would have a higher resale value than face value. We got caught by that, and we certainly underestimated the demand that would arise through the fan club. We did the best we could to meet it. But we'll be a little more careful next time."

Then, in the wake of the postponements in Japan and Australia, Fogel spent months dealing with insurance fallout. "That process took a very long time and was very difficult and complex, but ultimately resulted favorably," he says. "That probably was a much greater challenge than the actual logistics of bringing the production and personnel back together.

"We had a few venue issues [rescheduling] in Japan, because originally we were playing outdoors at Yokohama Stadium," he adds. "Given we were now in early December, the weather is such that we had to then look to go indoors. So, we had to basically refund 60,000 tickets and then resell for three shows at an arena."

But, to the surprise of nobody, the fans were still right there waiting to attend the makeup dates. "In Australia, even though we were postponing the shows by six months or so, almost no customers asked for a refund," McGuinness says. And indeed, the time off allowed U2 to rejigger the tour set list, as well as record "The Saints Are Coming" and the new song "Window in the Skies" with producer Rick Rubin. Both were released on the compilation "U218 Singles" in November.

Summoning inspiration for new material never seems to be a problem for U2. How long it takes to translate those ideas to tape is another matter.

"I always try and have a guitar around, because you never know when a song is going to hit you over the head," the Edge told Billboard in an interview last November. "I subscribe to the Keith Richards theory of having a guitar by the head of your bed when you're asleep, because you might wake up and you just never know."

Vertigo has also spawned a DVD, "Live in Chicago," which is the top-selling U2 DVD with sales of 285,000 copies in the United States, according to Nielsen SoundScan.

While it may have been tempting to entertain adding still more shows to the itinerary after the fall leg, McGuinness says this was "a logical point to stop. We're obviously aware we could go on and on and on, but selling out is actually more important to us than the gross."

So where does the U2 touring behemoth go from here? The first step is the band returning to the recording studio, which it will do sometime next year with an eye on releasing a new album by the end of 2007. McGuinness predicts the next tour will then begin in 2008.

"All I can say is it will be completely different the next time, but it will be big," he says. "I think our audience expects very big productions. We've become good at doing that, and I think it is part of U2's reputation." The band may even experiment with commercially releasing select concerts as downloads shortly after their completion. "That's something we're exploring," McGuinness acknowledges. "In the future there will be more what we call 'band-to-fan activity.' "

One thing that won't change is the alliance between McGuinness and Fogel. "Their organization contains extraordinary expertise," McGuinness says of TNA. "That is really the key to it -- knowledge of venues and markets absolutely worldwide. I really can't imagine doing a U2 tour without it."