The world's most populous country will become its biggest smartphone market by year-end, market researcher IDC estimates. It may account for 26.5 percent of all shipments compared with only 17.8 percent for the U.S.

Besides new carriers, IDC said one reason China will take the lead will be lower costs, especially in the sub-$200 category, for smartphones operating on the Android OS from Google (Nasdaq: GOOG), the No. 1 search engine.

Last year, IDC said, the U.S. accounted for 21.3 percent of global share, with China holding 18.3 percent. China's surge "does not mean that the U.S. smartphone market is grinding to a ahlt,"
 said Ramon Llamas, senior IDC analyst. "Growth is expected to continue but at a slower pace."

Meanwhile, IDC estimated the UK will account for 4.5 percent of this year's share, followed by India, with 2.5 percent and Brazil, with 2.3 percent. By 2016, China's share will be 23 percent, followed by the U.S., with only 14.5 percent share.