Woman sitting on steps with smartphone © Image Source, Image Source, Getty Images

You grab your phone for texts, pictures, music, games and movies. How about using it to save a few bucks?

A growing number of consumers are using their mobile devices to shop, with mobile-commerce sales in the United States expected to jump to $38.8 billion in 2013, a 56% increase over 2011, according to eMarketer.com. Mobile commerce already represents nearly 15% of online retail sales, a figure expected to rise to 24% by 2016.

Today, the bulk of mobile retail sales are music downloads, games or other digital goods. But sales of physical items such as home electronics, DVDs – even coffee – are growing rapidly, says Clark Fredricksen, an eMarketer vice president.

"What you're seeing is more people making purchases while they're standing in a store or a deal flashes up in an email and they decide to buy it right then and there," Fredricksen says.

Not surprisingly, even many neighborhood stores now offer mobile-based digital coupons, loyalty programs, in-store specials and other enticements to get customers in the door.

Some apps use location-tracking technology to find customers as they enter a restaurant or shop, or when they drive within a certain radius of a store. Others aggregate data on a customer's past purchases to offer deals on relevant merchandise or services.

Here are some mobile apps and services that can help you find bargains:

Rewards programs

Rewards apps are one way retailers are trying to reverse "showrooming," the practice of shoppers checking out a product in a brick-and-mortar store but ultimately buying it cheaper online. Shopkick, available for iPhone or Android, gives you points called "kicks" every time you visit a store or buy something. Earn enough kicks, and you can redeem them for coffee, movie tickets and other goodies. Among the participating brands are Crate & Barrel, Old Navy, Wet Seal, Target, Macy's, Sports Authority, Best Buy, Exxon and Mobil.

"They're very clever in terms of connecting with a smartphone browser, getting them into the store and reminding them of things they'd like," says Catherine Boyle, an eMarketer senior analyst.

Store apps

Retailers such as Wal-Mart, Target, Walgreen and Home Depot have their own apps to deliver targeted advertising to shoppers. For example, the Wal-Mart mobile app, available for iPhone, iPad and Android devices, lets shoppers check on so-called rollback discounts and set up notices of upcoming sales events.

IPhone owners can also use it to find out where toothpaste, frozen pizza, dog food and other merchandise is located in their local Wal-Mart. Still, in-store apps have some challenges to overcome. For one, shoppers must use Wi-Fi or Bluetooth connections for some of the features to work, Boyle says.

Geo-fencing

Some retailers and brands use a location-aware technology called geo-fencing to draw invisible boundaries around specific areas and deliver marketing messages to consumers as they walk, bike or drive into the zones. A retailer, for example, could create a block-long geo-fence around his ice cream shop so when a potential customer walks by on the sidewalk, a 20% off coupon flashes on their phone.

Twitter is working on a geo-fencing application for retailers that could be ready in time for the holiday shopping season, according to Ad Age. Some retailers and brands deliberately place ad messages within geo-fenced zones around their competitors. In those cases, ads have to be worded just right to lure shoppers away from competitors "without being creepy," Boyle says.

Text messages

Smartphone-based deals aren't just about apps and ads on mobile websites. Mobile marketing services can help retailers with limited marketing budgets reach customers through SMS or text messages. One service is Cellit Spark, which retailers can use to text customers coupons or alerts about upcoming sales.

Location-based apps and other bargain apps are not without their detractors. Consumer advocates worry such services could be invading customers' privacy. One simple remedy is to change your phone's settings to turn off your location. Apps also need your permission to send you push notifications of deals, and you can always decline those requests, Boyle says.

On a broader level, industry organizations such as the Mobile Marketing Association have come out against aggregating information on individual shoppers. But in surveys, Boyle says, shoppers have indicated a willingness to share their location in exchange for something they value: deals.

Click here to become a fan of MSN Money on Facebook

More from Michelle V. Rafter: