This morning on NPR Wendy Kaufman said there are over 300M cell phone users in the US. This is an implausible claim on the face of it, so I decides to look at the numbers. First, the census bureau estimates about 312M people in the US. Infoplease estimates just over 300M cell phone users in the US in 2010, http://www.infoplease.com/ipa/A0933563.html. So are we to believe that 96% of Americans have cell phones? Including small children, the very poor, and the elderly? Infoplease says their source is CTIA—The Wireless Association, but they don't give a link or anything else. Still, since Infoplease was the first result in my Google search, it's quite possibly the sole source of a typically poorly-researched NPR story. My guess is that the 300M number is really the number of cell phones in the US, not the number of cell phone users. But that's just a guess. My other observation is that it comes from an industry body, so it may very well be an over-estimate, counting, e.g., dead phones in drawers, etc.
The NPR story: http://www.npr.org/2012/04/08/150230250/a-brief-history-of-the-mobile-phone