The latest report from market research company The NPD Group (NPD) shows Android continuing to hold on to its crown as the dominant operating system in the U.S. smartphone market. Android was on 52% of smartphone units sold in the second quarter of this year, according to NPD.

Experiencing “slight” growth in market share, Apple’s iOS trailed behind at second place with 29% market share in the same quarter. Research in Motion’s BlackBerry OS’s share dipped to 11%, while Windows Phone 7, Windows Mobile, and webOS remained in their places at less than 5% share each.

Growing Prepaid Smartphone Market

NPD also noted a big jump in growth in the prepaid smartphone market. About one of five new handset purchases in Q2 2011 was tied to a prepaid plan. In Q2 2010, prepaid smartphones only comprised 8% of the market for prepaid phones. That grew to 22% in Q2 2011.

Motorola, the patent-rich hardware maker which Google recently brought into its fold, still has a heartbeat, although the figures seem to portray it as faint and feeble. Motorola’s overall mobile phone market share fell by 3 percentage points–9% in Q2 2011 from 12% in Q2 2010. Its share in the smartphone market also declined by the same amount of percentage points–from 15% down to 12%. Motorola’s unit share of Android smartphone sales in Q2 this year was just half (22%) of its share in the same quarter last year (44%).

Opportunity for Motorola

But, there seems to be hope for Motorola. NPD’s executive director of industry analysis, Ross Rubin, sees in the growing prepaid smartphone market a possible opportunity for Motorola to reclaim some of the glory that it lost. “This was once a key segment for Motorola that the company has an opportunity to reclaim as prepaid carriers build their smartphone portfolios,” Rubin said.

Rubin explained that “Motorola is experiencing increased competition from Samsung and LG in the smartphone market.” Rubin expressed hopes of recovery for Motorola, especially with Google’s recent buyout of the company. “Closer ties to the heart of Android can help inspire new paths to differentiation,” said Rubin.

As to how Motorola will be taking advantage of its “closer ties to the heart of Android,” let’s wait and see. Do you think Google can resuscitate Motorola’s slow market performance?