Smartphone shoppers made this holiday season a milestone for mobile sales. (JAY DIRECTO/AFP/GETTY IMAGES)

E-commerce is so last year. This holiday season, nearly one in five holiday shoppers played Santa on a new device — their phones.

Stores may remember 2012 as the breakthrough year for mobile with several major retailers reporting huge jumps in their sales made through smartphone devices this season.

With three shopping days left in the season, Wal-Mart already expects mobile to drive 40 percent of its online holiday traffic. eBay reports that one in every three shoppers use mobile devices to buy or research their products. And Gilt Groupe, the high-end bargain site, says one-third of its customers shop on phones, and revenue from mobile doubled this year.

An recent report from IBM found that 16 percent of shoppers bought something on their phone this Black Friday alone.

“Mobile is definitely one of our key strategic goals right now,” said Jason John, Gilt’s vice president of online marketing. “I wouldn’t be surprised if 50 percent of our sales came from phones and tablets at this time next year.”

It should come as no surprise that mobile sales are up — mobile is up, too. A September report by the Pew Internet & American Life Project found that nearly half of American adults own smartphones.

Statistics like these have inspired many retailers to court their phone-savvy customers more aggressively. Wal-Mart, for instance, has begun to offer special promotions exclusively to mobile shoppers, such as the 40-percent discount on popular gifts the company offered last weekend.

Now retailers are looking for ways to further engage customers on apps and mobile Web sites. Jason John, the Gilt marketer, said the company is working on the notification systems for its phone and tablet apps to better alert customers when products go on sale. Toys ‘R’ Us redesigned its mobile app earlier this year to promote more in-store engagement.

Whatever retailers are trying, mobile sales are virtually guaranteed to keep growing next year — after all, thousands of potential shoppers will unwrap new smartphones in just a few days.