According to a Nielsen report released on Monday, Google’s open-source Android operating system increased its market share to 27 percent over the past six months, while Apple’s iPhone platform declined to 23 percent of the market. Another report released Monday by Canalys, a research firm, estimates that nearly five million Android smartphones were sold in the U.S. last quarter, compared with about 3.2 million iPhones. Of course iPhone 4 didn’t launch until the end of the quarter, but Google’s recent dominance should have Apple and RIM, maker of the Blackberry, concerned. According to Business Insider, it’s a sign that Apple should make the iPhone available from more carriers in order to remain competitive. Despite Android’s increased popularity, the Nielsen report mentioned that 90 percent of iPhone customers remain loyal to the phone, while 21 percent of Android users and 29 percent of Blackberry owners have thought about converting to another phone. Canalys estimates that the entire smartphone market grew 64 percent in the second quarter.