17% of US mobile owners do most of their web browsing on their phones

"17% of cell phone owners do most of their online browsing on their phone, rather than a computer or other device. Most do so for convenience, but for some their phone is their only option for online access.
Some 88% of U.S. adults own a cell phone of some kind as of April 2012, and more than half of these cell owners (55%) use their phone to go online. We call these individuals “cell internet users” throughout this report, and this represents a notable increase from the 31% of cell owners who said that they used their phone to go online as recently as April 2009.
Moreover, 31% of these current cell internet users say that they mostly go online using their cell phone, and not using some other device such as a desktop or laptop computer. That works out to 17% of all adult cell owners who are “cell-mostly internet users”—that is, who use their phone for most of their online browsing."

Source:  Report from Pew Internet & The American Life Project, 26th June 2012

Methodology:  "These are the findings from a national telephone survey conducted March 15-April 3, 2012 among 2,254 adults age 18 and over, including 903 interviews conducted on the respondent’s cell phone. Interviews were conducted in English and Spanish. The margin of error for all cell phone owners (n=1,954) is plus or minus 2.6 percentage points, and the margin of error for cell phone owners who go online using their phones (n=929) is plus or minus 3.7 percentage points."