CHICAGO - Keep computers in a common area so you can monitor what your kids are doing.

It's a longstanding directive for online safety - but one that's quickly becoming moot as more young people have mobile devices, often with Internet access.

A report from the Pew Internet & American Life Project finds that 78 percent of young people 12 to 17 now have cellphones. Nearly half of those are smartphones, a share that's increasing steadily - and that's having a big effect on how, and where, many young people are accessing the Web.

The survey, released Wednesday, finds that 1 in 4 young people say they are "cell-mostly" Internet users, a percentage that increases to about half when the phone is a smartphone.

In comparison, just 15 percent of adults said they access the Internet mostly by cellphone.

"It's just part of life now," says Donald Conkey, a high school sophomore in Wilmette, Ill., just north of Chicago, who is among the many teens who have smartphones. "Everyone's about the same now when it comes to their phones - they're on them a lot."

He and other teens say that if you add up all the time they spend using apps and searching for info, texting and downloading music and videos, they're on their phones for at least a couple of hours each day - and that time is increasing, they say.

"The occasional day where my phone isn't charged or I leave it behind, it feels as though I'm naked in public," says Michael Weller, a senior at New Trier High School, where Conkey also attends. "I really need to have that connection and that attachment to my phone all the time."

According to the survey, girls 14 to 17 were among the most likely to say their phones were the primary way they access the Web. And while young people in low-income households were still somewhat less likely to use the Internet, those who had phones were just as likely - and in some cases, more likely - to use their cellphones as the main way they access the Web.

It means that, as this young generation of "mobile surfers" comes of age, the way corporations do business and marketers advertise will continue to evolve, as will the way mobile devices are monitored.

Already, many smartphones have menus that let parents block certain functions or mature content. cellphone providers have services that allow parents to see a log of their children's texts. And there are a growing number of smartphone applications that at least claim to give parents some level of control on a phone's Web browser, though many tech experts agree that these applications can be hit-or-miss.