During the three-month period ending in January, Google’s (GOOG) Android operating system once again surpassed iOS in U.S. smartphone sales thanks to the help of an unlikely partner. According to Kantar Worldpanel, Android smartphone sales at Sprint (S) helped the operating system climb 6.4 percentage points to account for nearly half, or 49.4%, of all U.S. smartphone sales. In the same period, iPhone sales dropped 4.7 points from a year ago to make up 45.9% of U.S. smartphone sales, while sales of Windows Phone’s share increased to 3.2%.

“Part of Android’s increase in the latest period can be attributed to its large gain in share within Sprint’s smartphone sales,” Kantar Worldpanel analyst Mary-Ann Parlato said. “In the three-month period ending October 2012, sales on Sprint were divided almost 50/50 between Android and iOS. However, in the latest period, Android’s share of Sprint sales increased by 22.6% points from 49.3% to 71.9%.”

Parlato noted that previously both iOS and Android smartphones shared similar average retail prices, however the most recent period saw “a significant price drop to $95 for Android, while iOS increased slightly to $146.”

The Galaxy S III accounted for 14% of all smartphones sold on Sprint’s network in October. Sales increased to 39% during the three months ending in January and are still growing thanks to a price drop from $199 to $99 over the holiday season. On T-Mobile, the only other major carrier where Android is consistently the top-selling operating system, Samsung’s (005930) flagship smartphone represented only 18% of sales in the most recent quarter.

Samsung handsets accounted for 60.3% of all smartphones sold on Sprint in the January period but despite Android and Samsung’s gains, Sprint’s sales only grew 0.8% year-over-year.