As a teenage rock fan, all Dennis Vorreyer really expected of the Lollapalooza music festival in Chicago two weekends ago was the chance to see his favorite bands perform live.

    But he and his father, Jeffrey, who accompanied him to the festival, signed up for Lollapalooza's text-message network, and thus learned about a guitar-playing contest taking place there. Dennis, 14, entered and won a new Gibson guitar. Tad Kubler, the lead guitarist for the Hold Steady, who was involved in the contest, then invited Dennis to perform with the band as it closed its set.

“Having your cell phone everywhere is important for everybody now,” Dennis said. “I never dreamed of playing Lollapalooza.” The modern mobile phone — equipped with camera, Internet access and more— has proved to be aliabilityfor some performers, like Akon and Beyonce, whose regrettable moments were captured by fans and then immortalized on YouTube and similar sites. But for the fans themselves, mobile phones are becoming as important an accessory as an all-access wristband. Beyond using them to record a short souvenir, they are becoming a ticket to everything from free ringtones to VIP treatment.

    On Gwen Stefani's recent tour, as many as 20 percent of the audience at some shows agreed to pay 99 cents for text messages and the chance to win better seats, according to the mobile marketing company Impact Mobile. At festivals like Lollapalooza, thousands of fans sign up to receive continuous updates from concert organizers about promotions and special events.

Even when there is no fee, the service comes at a price: fans must give their phone numbers to marketers. And purists — and some artists — disapprove of fans pecking out text messages or snapping pictures during performances. Still, the arrival of a new generation of phone-based activities could add a new twist to live events at a time when rising ticket prices have discouraged many concertgoers.