The report by comScore, a study of mobile behavior, found Google sites attracted 93 million of the 97 million Americans using their smartphones for the Internet.

Next was Facebook with 78 million, followed by Yahoo! (66 million) Amazon (44 million) and Wikimedia, which includes the Wikipedia site (39 million).

But it also found that 80 percent of time spent was represented by "app" usage compared to 20 percent via browser.

Twitter saw an even higher percentage of time spent with apps at 96.5 percent of all minutes.

The most popular app was Apple iTunes with 32 million users, followed by Google Maps with 29 million and Facebook with 26 million.

Social networking was a particularly popular activity on smartphones, and Facebook led the pack, with the average Facebook mobile user spending more than seven hours via browser or app in March.

Pinterest, which has seen its adoption explode in recent months, reached 7.5 million smartphone visitors who used the brand for nearly an hour.

Location-based social network Foursquare attracted 5.5 million mobile visitors at an average of nearly 2.5 hours, while Tumblr reached an audience of nearly 4.5 million who engaged for 68 minutes during the month.

A study released Monday shows people using their mobile devices increasingly to settle a dispute, coordinate a meeting, find a restaurant or get emergency information.

The Pew Internet & American Life Project said 70 percent of all cell phone owners and 86 percent of smartphone owners have used their phones for one of seven key activities, which include solving an unexpected problem, getting directions or learning the score of a sporting event.

"Overall, these 'just-in-time' cell users, defined as anyone who has done one or more of the above activities using their phone in the preceding 30 days, amount to 62 percent of the entire adult population."

The younger users are even more reliant on their mobile devices: 88 percent of those ages 18-29 had performed one or more of these activities in the past 30 days, compared with 76 percent of the 30-49 age group, 57 of those ages 50-64, and 46 percent of the owners age 65 and older.

Some 31 percent of men use their phones to look up information that settles an argument or disagreement, compared with 22 percent of women, the study found.

And some 65 percent of smartphone owners say they have used their phone to get turn-by-turn navigation or directions while driving, with 15 percent doing so on a typical day.

The survey conducted between March 15 and April 3, 2012 among 2,254 adults found that 88 were cell phone owners and 46 percent had smartphones.