According to emarketer Smartphone Adoption Tips Past 50% in Major Markets Worldwide

More than half of Americans now own a smartphone, according to the latest poll by the Pew Internet and American Life Project.

Nielsen MOBILE MAJORITY: U.S. SMARTPHONE OWNERSHIP TOPS 60%

Canalysis  Smart mobile device shipments exceed 300 million in Q1 2013

comScore Reports April 2013 U.S. Smartphone Subscriber Market Share

Asymco Measuring US Mobile Platform Shares: Kantar vs. comScore
Asymco Measuring Platform Churn