According to latest survey results released on Monday by Nielsen, "Smartphones now represent 37% of all U.S. mobile phones -- and smartphones running Google's Android operating system are the most popular of all."
"After having raced to the No. 1 spot in less than a year -- climbing from a 15% share in June 2010 to 37% in March 2011 -- Google held steady at 36% in the three month period from Feb. to April 2011."
"Apple also held steady -- its market share over the past 3 months weighed in at 26% -- within a few points of where it's been in Nielsen's surveys for more than a year. Even RIM's BlackBerry may have started to slow its long decine, settling in at 22% to 23%."
Although iPhone owners are more likely than Android aficionados to download apps, stream music or watch videos, individual Android users who do that kind of stuff tend to download much more data (582Mb/user), compared with 492 MB for iPhone owners. See charts below: