The mobile revolution has reached another milestone: Consumers now spend more time interacting with online retailers on smartphones and tablets than they do on desktops and laptops.

55% of all time spent with online retail in June 2013 occurred on a mobile device, finds web and mobile measurement firm comScore. 45% occurred on desktops and laptops. Specifically, smartphones accounted for 44% of retail Internet minutes while tablets accounted for 11%, comScore says.

“Since U.S. consumers now spend more than half of their time on retailers’ web sites using their smartphones and tablets, mobile can’t be viewed simply as an ancillary device or action, it now epitomizes how consumers think and act when they interact with retailers,” says Shop.org executive director Vicki Cantrell. Shop.org is the National Retail Federation’s online division. “Retailers have to continue to invest to make sure they get their mobile offerings right, or will increasingly risk alienating customers and leaving significant money on the table.”

ComScore released its new mobile commerce findings today at the Shop.org conference in Chicago. ComScore worked with consulting firm The Partnering Group on this mobile report.

When it comes to making purchases online, 69% of desktop shoppers, 34% of tablet shoppers and 21% of smartphone shoppers made at least one purchase online in Q2 2013, comScore says.

Online consumers use their smartphones and tablets for many shopping-related activities. In Q2 2013, 57% of smartphone users while in a retailer’s store visited that retailer’s site or app compared with 43% who consulted another company’s site or app, comScore says. The top reason consumers consulted retailers’ sites or apps was to compare prices. Among those smartphone users who went to the same retailer’s site, 59% wanted to see if there was an online discount available, the report says. Similarly, among those who checked a different retailer’s site, 92% wanted to see if they could get a better deal on price.

Smartphone owners also used their devices while in stores to take a picture of a product (23%), text or call family or friends about a product (17%), and send a picture of a product to family and friends (17%).

The comScore mobile commerce report also finds that:

• 35% of smartphone owners in Q2 2013 used their device to locate a store, 24% to find coupons and deals, and 19% to look up product availability.
• Nearly two-thirds of smartphone owners in Q2 2013 used a mobile web browser to research product features (64%), and more than half used a mobile web browser to find a store location (59%) and to find coupons and deals (53%).
• Apparel and accessories (37%) and event tickets (25%) were among the top products smartphone shoppers bought with their devices during Q2 2013.

“Mobile is having a profound effect on how people engage with the retail experience today,” says Lynée Alves, director of retail solutions at comScore. “Not only are consumers using their mobile devices to engage more with retail sites and apps, they are also beginning to transact on these devices in a meaningful way. The m-commerce revolution is building momentum, and retailers must adapt to this new landscape if they are to succeed in this emerging channel.”

But while U.S. consumers spend the majority of time interacting with retailers online via mobile devices, they are not making an equivalent number of purchases. In 2013, mobile retail sales for the 358 U.S. merchants ranked in the 2014 Internet Retailer Mobile 500 plus mobile sales through eBay Inc. will grow about 64% to $34.2 billion, according to the Mobile 500. That’s 13.2% of estimated total 2013 e-retail sales of $260 billion, Internet Retailer says.

The fundamental reason for the difference between time spent and sales is that smartphones account for the vast majority of time spent with e-retail on mobile–four times more than tablets–and mobile shoppers primarily use smartphones to research stores and products, retailers and research firms say. And when smartphone shoppers do buy, they spend 18% less than tablet shoppers–$106 versus $125 average tickets, the Mobile 500 says.  What’s more, smartphone shoppers spend 88% less than all web shoppers combined–$106 versus $199 average tickets, according to the 2013 Internet Retailer Top 500 Guide.

For example, the average ticket for a Crate & Barrel tablet shopper is $174, versus $127 for a smartphone shopper, the merchant tells Internet Retailer. 80% of the retailer’s mobile sales come from tablets while only 20% stem from smartphones, it says. The conversion rate for tablet shoppers is 2.35% and for smartphone shoppers 0.92%, the merchant reports. The average conversion rate for all web shoppers at the top 500 e-retailers is 3.29%, according to the Top 500 Guide.

“Smartphone shoppers are looking at our e-mails whenever they have downtime, and they just get snippets of stuff as they look up answers to questions or start the shopping process and get ideas, then finish it off later on the desktop,” says John Seebeck, vice president of e-commerce. “Smartphones are also used for in-store research. And recently our smartphone usage has shifted to a less affluent demographic.”