If retailers don't have a mobile-optimized website, now is the time to at least consider one. According to new data from Walker Sands Communications, more than one in 10 consumers browse the web from their mobile devices.

In the fourth quarter of 2011 alone, 13 percent of all website traffic came from on-the-go consumers, marking a sizable increase from the 6 percent observed during the same time period the previous year. This is particularly the case among shoppers using Apple devices – 47 percent of mobile traffic stemmed from the iPhone, iPod or iPad.

"When we began this study in Q3 2010, traffic originating from mobile devices accounted for a relatively modest portion – 4 percent – of total web traffic," says John Fairley, director of digital services at Walker Sands. "More than a year later, we have seen a significant uptick in mobile browsing, which has increased more than three-fold."

According to separate data from comScore, approximately 91 million Americans currently own smartphone devices. This number doesn't include the millions of prospective customers that own tablets.