37% of American adults claim to own a smartphone

"Driven by demand for the Palm Pre and new Apple iPhone devices, smartphone ownership is continuing to rise, with 37% of US consumers now reporting they own some type of smartphone, according to a June survey by ChangeWave Research.
The survey also found that 14.4% of respondents say they plan to buy a smartphone in the next 90 days - up one-third from a year ago (10.5% in June 2008) and the highest percentage ever recorded in a ChangeWave survey."
Source: ChangeWave Research, June 2009, reported by MarketingVox 24th July 2009
Note: I'd treat this with a little bit of caution - I'm mnor sure how tight the definition of Smartphone was in the survey - could people have interpreted it as any phone with internet access?