Apple iOS up, Android flat, RIM down among recent acquirers.

Smartphones continue to grow in popularity. According to Nielsen's May survey of mobile consumers in the U.S., 38 percent now own smartphones. And 55 percent of those who purchased a new handset in the past three months reported buying a smartphone instead of a feature phone, up from 34 percent just a year ago.

Android continues to be the most popular smartphone operating system, with 38 percent of smartphone consumers owning Android devices. However, while Android also leads among those who recently purchased a new smartphone, it is the Apple iPhone that has shown the most growth in recent months.