Apple iPhone's second-place share also increased by 4 percent to give it a 27 percent share, according to the survey of 30,000 U.S. subscribers for the three months ending in July. The prior period ended in April.
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Meanwhile, Research in Motion and Microsoft saw declines in their market shares. RIM, maker of the BlackBerry, declined by 15 percent over the three-month period to 21.7 percent and stayed in third place. Microsoft, which makes the Windows Mobile and Windows Phone mobile operating systems, stayed in fourth place with nearly a 15 percent decline for a 5.7 percent market share.
A drop in market share does not necessarily mean a vendor sold fewer smartphones than three months earlier, since the smartphone market is growing impressively. In July, ComScore noted that 82.2 million people in the U.S. owned smartphones, an increase of 10 percent from the prior three-month period.
For all mobile devices, including smartphones and lower-end feature phones, ComScore reported 234 million customers in July, led by Samsung (25.5 percent share), LG (20.9 percent), Motorola (14.1 percent), Apple (9.5 percent) and RIM (7.6 percent).
Texting was the most popular use of mobile devices by 70 percent of users when compared to several other uses: browsing (41 percent), use of downloaded apps (40.6 percent), use of a social networking site or blog (30 percent), game-playing (28 percent) and listening to music (20 percent).
Read more about smartphones in Computerworld's Smartphones Topic Center.