According to a recent ComScore survey, 49.1 million people in the U.S. owned smartphones during the three months ending in May, up 8.1 percent from the corresponding February period. This is equivalent to 20.1 percent of total users. A previous survey from December showed 17 percent penetration.
In a previous article I pointed out that more than 1 million Americans are switching to smart phones every month. This number is now 1.2 million per month. The number of non-smart devices in use is 185 million and at current rates smartphone users will outnumber non-smart users in 4.5 years. With a very small acceleration I reckon less than 4, or by 2014.
(posting from my iPad)