Downloads of mobile games grew 17% last year thanks to the increased graphics capabilities of smartphones like Apple's iPhone, according to a report from ComScore.

The report said 8.5 million people, or 3.8% of mobile subscribers, have downloaded a game to their cell phones. While ComScore's game charts used to be dominated by handsets like the Motorola Razr, smartphones like the iPhone and BlackBerry devices are quickly rising up the charts.

"The rapid growth in smartphone adoption in the United States has provided a boost for mobile gaming, as 34% of those downloading a game in November did so using a smartphone," ComScore senior analyst Mark Donovan said in a statement. "Last year, not one smartphone appeared in the top 10 devices used for mobile downloads. This year six out of 10 are smartphones, excluding devices with smartphone-like functionality, such as the Instinct and Voyager, which also make appearances."

With its touch screen, robust processor, and 3-D graphics capabilities, it's no surprise that the iPhone 3G has been a hit with gamers. Apple iPhone owners accounted for 14% of mobile game downloads, ComScore said. Overall, 32.4% of iPhone users have downloaded a game, compared with a market average of 3.8%.

One reason iPhone owners are more likely to download games is the tight integration of the App Store, which makes browsing, buying, downloading, and installing games easier than on alternative platforms. This success has well-known game developers like Electronic Arts, Sega, and LucasArts hoping to capitalize on this market.

While the iPhone is leading the way, ComScore has seen a considerable uptick in mobile gaming on platforms like BlackBerry, Symbian, and Windows Mobile. Overall, the mobile gaming market could top $4.5 billion this year, although the rough economy may be a hurdle.

"As the mobile phone has evolved into a better platform for both playing and merchandising games, the games being offered have also been improved, drawing in a broader user base," said Donovan.