MIAMI - Loyalty cards have changed a lot in recent years, moving from paper to plastic and now to nothing but data kept on a cell phone, the New York Times reports. More retailers are embracing mobile loyalty cards as an inexpensive way to reward shoppers instantly.

Companies like CardStar and CardBank revert existing loyalty card data onto cell phones with barcodes that can be scanned. Other businesses like Motorola and mFoundry are giving merchants the technology to create their own mobile loyalty cards. And some companies are looking to the future by developing ways cell phones can be used to bring the digital and physical worlds together.

For example, the Loopt, a service allows users to share their location with friends via their cell phone, has branched out with Loopt Star that rewards users for stopping by certain places on a regular basis. The Loopt Star game has attracted interest from Universal Music, Gap and Burger King, which will be using the game to award incentives to loyal shoppers.

"Instead of advertising with a banner, it??s offering users incentives for good behavior," said Sam Altman, Loopt??s co-founder and CEO. "They??re trying to turn existing customers into better ones."

Foursquare also has a location-sharing game that businesses like Pepsi and Tasti D-lite use to reward and keep track of customers. Some companies use more than one mobile application to stay in touch with customers, such as Starbucks, which has Loopt Star, Foursquare and its own iPhone loyalty card.