Nine million US consumers, or 3.6% of mobile users, have made a purchase using their mobile phone, according to new research from Nielsen Mobile. The data also show that 49% of mobile consumers plan to join the m-commerce party in the future.

Nielsen found that men are more likely than women to use their phone for commerce - 4.5% versus 3%. Also, a larger percentage of consumers in the 25-34 age group - 5.4% - have paid by mobile than the mobile population overall.

The most popular ways to make a purchase with a cell phone are mobile Web sites, of which eBay is the most popular, and via text messaging. Of the nine million who've participated in m-commerce, 6.5 million have used text messaging to purchase an item, Nielsen says.

So, why aren't more people trying it? Of the folks who have yet to make a purchase over mobile, 41% said concern for security is their biggest concern. Some 23% worry over airtime charges and 21% don't trust that the transaction will be completed.

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