Two-thirds of new mobile phone purchases in the US during a three-month period ending in June were smartphones, according to new stats from Nielsen, as adoption cruises past the tipping point. Some 54.9% of US mobile subscribers now own a smartphone, and the battle for market domination continues to look like a two-horse race between GoogleGoogle’s Android OS and Apple’s iPhone. Android is still the runaway leader, controlling half of the US market, though Apple accounts for more than a third of it with 34.3%. The stats are in contrast to recent Enders Analysis figures, which claim that the iPhone comprised half of US smartphone sales in Q1, ahead of 36% for Android. Nearly 55% of all smartphone purchases during the last three months were Android-based, with 36.3% of consumers opting for an iPhone. The stats are grim for RIM, with BlackBerry smartphones accounting for just 4% of new purchases during the period.

Samsung is leading Android’s US charge, accounting for 17% of the US smartphone market. Samsung’s share is perhaps further behind Apple than some analysts would expect, with many claiming that the South Korean firm is neck and neck with the iPhone manufacturer as the pair vie for the title of the world’s biggest smartphone vendor. Recent research from ABI claims that Apple and Samsung account for 90% of global smartphone profits, illustrating the pair’s emerging dominance.

Despite its recent struggles, HTC remains the second-largest Android vendor in the US, accounting for 14% of the software’s market share. The Taiwanese firm also gained an extra 2.9% of the market thanks to its smartphones that run on Microsoft’s old Windows Mobile OS, plus 0.5% for its current Windows Phone software. HTC has struggled to keep pace with the rapidly-changing smartphone market in recent months, after briefly holding the top smartphone manufacturer spot last year.

Nokia continues to struggle at the foot of the US smartphone market, accounting for a combined 1.2% of the market. Its Symbian OS, accounts for just 0.9% as the firm continues to focus primarily on Windows Phone. Nokia’s Windows-based smartphones account for 0.3% of the US market, gaining on rivals HTC and Samsung, which have 0.5% each with their Windows Phone-based devices.

Overall, smartphone adoption continues to rise, with sales predicted to top 1bn by 2014, according to stats from Credit Suisse. However, emerging markets are set to play a more prominent role in future growth, with research from Canalys asserting that China surpassed the US to become the world's largest smartphone market during the first quarter, with the latter’s smartphone shipments growing just 5% year on year, indicating that the market could be reaching saturation.