Android was the only smartphone operating system that saw an increase in its share of the U.S. market in the third quarter, Nielsen said Thursday.

In the third quarter, smartphones running the Android OS were used by 43% of smartphone owners, up from 39% in the second quarter, according to Nielsen surveys of actual users.

Meanwhile, Apple, whose iPhone runs on iOS, remained the biggest single smartphone brand in the U.S. The iPhone had 28% market share in both the second and third quarters, Nielsen said.

The other smartphone platforms trailed Android and iOS: BlackBerry's U.S. market share was 18% in the third quarter, down from 20% in the previous quarter; Windows Mobile had market share of 7%, but Nielsen didn't say how the Windows Phone operating system did in the third quarter after gaining just 1% in the second quarter. All other operating systems combined accounted for 4% of the market in the third quarter.

Nielsen also found that adults aged 25 to 34 continued to be the biggest users of smartphones by far. Of people in age group who use either a feature phone or a smartphone, 62% use a smartphone. Smartphone penetration is about 54% among mobile phone users between the ages of 18 to 24 and 35 to 44.

This week, analyst firm Canalys said HTC shipped the most smartphones to the U.S. in the third quarter, delivering about 5.7 million units. HTC was followed by Samsung, which shipped 4.9 million units and Apple, which shipped 4.6 million iPhones.

Globally, HTC finished fourth in third-quarter smartphone shipments, with 13.2 million. Samsung was the global leader, shipping 27.3 million smartphones in the quarter. Apple shipped 17.07 million smartphones and Nokia shipped 16.8 million, Canalys said.

Matt Hamblen covers mobile and wireless, smartphones and other handhelds, and wireless networking for Computerworld. Follow Matt on Twitter at @matthamblen, or subscribe to Matt's RSS feed. His email address is mhamblen@computerworld.com.