Google (NASDAQ:GOOG)'s operating system Android dominates the world, while Apple (NASDAQ:AAPL)'s iOS maintained its dominance in the U.S. market.

Worldwide, Android devices has a market shares of 30% according to data released by the IDC. On the other hand, the iOS trails at a far second with just 17% share of the global market.

But it appears that even in Apple's home turf, the U.S., Android is closing in on the former's dominance. According to data from market research company NPD group, Apple captured a 31% market share in the the U.S., with Samsung in a near second with 24%. That's just a lead of 7%.

With the momentum of Samsung, which accounts for 44% of Android devices, it's not too hard to imagine that Google's operating system will close this gap in a short time. For one thing, tablet sales for Samsung has gone up by as much as 117% with 2.4 million units sold.

Dominance in the U.S. smartphone market is fast becoming a toss between Apple and Samsung. Their combined smartphone unit sales "rose 43 percent between Q2 2011 and Q2 2012."

Unit sales for other brands fell 16 percent. Other brands in the top five for smartphones are HTC, with 15%, Motorola, with 12 % and LG with 6%.

Chart: Worldwide Smartphone OS Market Share, 2Q 2012 Author: IDC