U.S. consumers spent an estimated $168 million on mobile virtual goods in the last year, according to a new study from research firm Frank N. Magid Associates and mobile social gaming network OpenFeint.

Magid says more than 70 million Americans now own smartphones, or around 23 percent of the U.S. population. The firm believes that 45 percent of those smartphone owners play mobile games, and that 16 percent of them have purchased in-game virtual goods, spending an average of $41 per year on them.

While the firm's research indicates that 75 percent of smartphone owners in the U.S. have not bought virtual goods, it says 55 percent of them have shown an interest in buying them. Magid argues that the mobile virtual goods market is "poised for strong growth" as the number of games offering virtual goods ramp up.

The group also found that smartphone gamers download an average of 14 titles per year, paying for around four of them while acquiring the other ten for free. It notes that Americans are most likely to review app store rankings to discover new games but also rely on word of mouth and friend suggestions, too.

Magid and Aurora Feint revealed this data in the the first half of its two-part study Magid Media Futures 2010 Wireless and Consumers. It plans to publish the second half of its findings later this summer.

"Everybody knows free-to-play social gaming models on PC platforms have been making a killing but mobile virtual goods aren't as well understood," says Magid Advisors president Mike Vorhaus.

He adds, "With almost 20 percent of smartphone gamers already making purchases, there's a lot of room for the market to keep taking off as smartphones continue to increase in popularity."