35% of American adults have a smartphone

"In its first standalone measure of smartphone ownership, the Pew Internet Project finds that one third of American adults – 35% – own smartphones. The Project’s May survey found that 83% of US adults have a cell phone of some kind, and that 42% of them own a smartphone. That translates into 35% of all adults.
Our definition of a smartphone owner includes anyone who falls into either of the following two categories:
One-third of cell owners (33%) say that their phone is a smartphone.
Two in five cell owners (39%) say that their phone operates on a smartphone platform (these include iPhones and Blackberry devices, as well as phones running the Android, Windows or Palm operating systems).
Several demographic groups have high levels of smartphone adoption, including the financially well-off and well-educated, non-whites, and those under the age of 45."

Source:  Smartphone Adoption and Usage report, from the Pew Internet & American Life Project, 11th July 2011