Pew Internet Research has been keeping track of how often people are using their cellphones to go online, and as of April 2012, 55% of adults who own cellphones are using them to go online.
Pew research also points out that 88% of the adult population in the United States owns a cellphone. Statistically speaking, that means almost half (49%) the adult population is going online via cellphones to check email or use the internet for various purposes.
Sticking with the same theme, over 40% of the respondents from the study said they go online almost daily, or on a typical day. If you refer to the chart below, you can see this mobile internet access trend is growing fast.
Of course, Pew includes all the stats on these folks who are using their cellphones to go online. Take a look at their data on race, gender, income, and several other factors. As usual, they give us a very comprehensive view.