The mobile world is nearing a major milestone: Nearly half—48%—of all U.S. mobile phone users own smartphones as of January 2012, research giant Nielsen finds. That’s up from 36% in Q1 2011 and 23% in Q1 2010. The smartphone revolution continues barreling ahead at full steam, and changing the way consumers interact with the Internet.

Among other things, smartphones are changing the way people shop. 22% of U.S. smartphone owners have purchased merchandise on mobile commerce sites or apps, Nielsen finds in its study of 300,000 consumers who own mobile phones. 15% have placed a bid through an online auction, 12% have purchased tickets to events, and 10% have purchased digital music or videos.

But m-commerce is not just about transactions on mobile devices. M-commerce sites and apps can be powerful cross-channel selling tools. For example, 38% of smartphone owners browse products through mobile sites and apps, Nielsen finds. This can be in preparation for a trip to a store, or it can be an activity on the go, say while commuting on a train, to plan a later purchase on an e-commerce site on a desktop computer or in a physical store. Further, 32% read customer reviews on their smartphones. Some retailers encourage shoppers through signs in stores to access reviews on smartphones, hoping the mobile customer reviews will clinch a sale.

24% of smartphone owners search for and use online coupons, the Nielsen survey says. Retailers can use online coupons as a cross-channel play to boost sales while customers are in their stores. 22% of smartphone owners have scanned a bar code to obtain additional product information, such as videos or more details than can fit on an in-store sign or product tag. And 18% of smartphone owners have used location-based services, such as a GPS-enabled store locator, to find a store.

“The data is clear: Mobile devices are changing the way consumers shop,” says Nielsen president of strategic initiatives John Burbank. “And while we’re still in the early days, smart retailers are investing and learning now, ahead of the curve, in order to be best positioned to follow the consumer wherever she goes.”

On another m-commerce front, there’s a lot of talk about mobile wallets today, but few wallet offerings and extremely low adoption. Mobile wallets store debit or credit card information in an app and enable a consumer to pay for purchases in stores. Nielsen finds that 16% of smartphone owners who have downloaded a mobile app are extremely interested in using a mobile wallet. 18% are very interested, 24% are somewhat interested, 13% are slightly interested and 30% are not interested.

Nielsen broke down smartphone owners by age. 62% of mobile phone users age 18-24 own a smartphone, Nielsen finds. The rest of the findings are as follows: 66%, 25-34; 58%, 35-44; 45%, 45-54; 33%, 55-64; and 22% age 65 and older.