According to market research company, NPD Group, Google's Android operating system (OS) continues to dominate the US smartphone landscape, accounting for 52% of handset units sold in Q2 of 2011.

Apple's iOS also experienced slight quarterly growth, increasing its market stake to 29% in Q2. BlackBerry holding company Research In Motion wasn’t so lucky though, as BlackBerry OS’ share fell to 11%. Microsoft’s Windows Phone 7 OS and Windows Mobile, as well as HP’s recently discontinued webOS held steady at under 5% of the market each.

"Google's acquisition of Motorola shifts the balance of power in the handset-patent conflict between Google and its operating system competitors," said Ross Rubin, executive director of industry analysis for NPD. "Android's momentum has made for a large pie that is attractive to Motorola's Android rivals, even if they must compete with their operating system developer."

Motorola's overall mobile phone market share declined three percentage points, from 12% in Q2 2010 to 9% in Q2 2011. The XOOM and Atrix maker's share of the smartphone market also declined from 15% to 12%. Motorola's year-over-year unit share of Android OS sales halved from 44% in Q2 of last year to 22% in Q2 of 2011, in the wake of substantial gains by the Korean tech giants Samsung and LG.

"Much as it did in the feature phone market in the RAZR era, Motorola is experiencing increased competition from Samsung and LG in the smartphone market," Rubin said. "Closer ties to the heart of Android can help inspire new paths to differentiation."