61% of U.S. adult smartphone users made at least one purchase from their device in the last six months; and among those mobile buyers, 73% made four or more purchases, according to the 2nd Annual Mobile Shopping Survey from RadiumOne, an online and mobile advertising technology firm. And, in a surprising turn, the most active group of shoppers is not youngsters—36% of smartphone users ages 45-54 made a mobile commerce purchase, the survey of 320 U.S. adult smartphone users finds. The least active group among mobile buyers is consumers ages 18-24; only 15% of smartphone users in that age bracket made mobile purchases.

Half of mobile users surveyed clicked on a mobile ad in the last quarter, the survey says. Also, smartphone users are twice as likely this year over last to read a product review via mobile while shopping in-store (8.9% versus 18.7%), the survey says.

The key takeaway from the survey is that mobile has grown into a mainstream advertising and marketing medium with highly frequent consumer attention and participation, as the survey shows that more than one-third of smartphone owners use their phone 40 or more times each day, RadiumOne says. Marketers can not only consider mobile an effective awareness medium, but now, also a medium that drives consumers to act, the vendor says.

“The opportunities for brands to engage consumers at all points of the marketing funnel have finally reached mainstream scale, with mobile users engaged with their devices so frequently throughout the day, and using their devices throughout the sales-decision process,” says Gurbaksh Chahal, CEO and founder of RadiumOne. “Consumers do engage, provided brands reach them in the proper context and geography and recognize at what stage of the purchase cycle to engage.”

RadiumOne offers ad technology that enables retailers to run what it calls “programmatic advertising,” essentially running ads in response to consumer behaviors, actions and interests. RadiumOne determines these factors not through dropping cookies on web and mobile web users but through using anonymous identifiers based on users’ Internet Protocol addresses and user agents, which include technographic parameters such as web browser information and device identifiers.

Follow Bill Siwicki, managing editor, mobile commerce, Internet Retailer, at @IRmcommerce.