(AP) -- When it comes to accessing the Web over mobile devices, Americans are far behind their Internet-connected counterparts in Japan, South Korea and parts of Europe.

"We are a third-world country where mobile is concerned. The rest of the world is using mobile phones underground, to pay for a parking space blocks away, to buy a Coke from a vending machine," said Jeffrey Cole, director of the Center for Digital Future at the University of Southern California. "We in America are still having trouble getting our phones to (make calls)."

But this is slowly changing. The latest survey from the Center for the Digital Future, conducted last year, found that 25 percent of U.S. went online using their cell phones. That is up from 16 percent in 2008 and 5 percent in 2002.

"The is the single most valuable device in people's lives," Cole said. "It's becoming a device you use for virtually everything."

On average, people who go online using their cell phones did so for about 2.5 hours a week in 2009, up from 1.7 hours a year earlier. For most, this means getting small spurts of information, such as getting directions or checking who won a sports game, Cole said.

A separate study, from the Pew Internet & American Life Project, backs those findings. It found that 40 percent of U.S. adults used a mobile device to surf the Web, send e-mail or participate in instant messaging. Those figures from May are up from 32 percent in 2009.

And more people reported taking photos, playing games and listening to music on their compared with a year earlier, the Pew survey found.

Overall, Internet use continues to grow. Among other findings in USC's report, which is scheduled for release later this month:

- Americans reported spending more time on the Internet. In 2009, time spent online averaged 19 hours a week, up from 9.4 hours in 2000.

- More people are online than ever. In 2009, 82 percent of Americans said they use the Internet, up from 67 in 2000.

- 18 percent of Internet users said they stopped subscribing to the print edition of a magazine or newspaper because they can get the same content online.

- Not surprisingly, texting is most popular among young people: users under 18 sent an average of 81 text messages each day. This is up from 51 in 2008. Counting all age groups, texters sent an average of 38 messages a day, up from 23 a year earlier.

USC's telephone survey of 1,981 Americans over 12 was conducted in April 2009 and has a margin of error of plus or minus 2.2 percentage points. Pew's survey of 2,252 U.S. adults, conducted in May, has a margin of error of plus or minus 2.4 percentage points.