Walmart just announced a new trade-in program that will launch on Sept. 21, allowing customers to trade in their smartphones for credit toward a new device.

The new service will be available in more than 3,600 Walmart stores and Sam's Club locations across the U.S. and will provide immediate credit between $50 and $300 toward the purchase of a new smartphone.

A working, non-damaged iPhone 5, for instance, could fetch customers $300 in credit, a Samsung Galaxy S3 could be worth $175 and a Samsung Galaxy S2 could get $52, according to Walmart.

"Smartphones have become a part of our customers' everyday lives and as new devices launch more frequently, trade-in programs are becoming more popular," Steve Bratspies, Walmart's executive vice president of general merchandise, said in the press release.

"More and more, customers are choosing where they purchase new smartphones best on where they'll get the best value for their trade-ins. Our goal is to give them more value for their old devices and the lowest price for their new one - all part of our promise to be the best destination for wireless."

More than 100 devices will qualify for Walmart's new trade-in program. Keep in mind, however, that all phones must be undamaged and in good working condition to be eligible for a trade-in.

"Customers should bring their working smartphone to an associate in the electronics department at participating Walmart stores and Sam's Club locations. In partnership with CExchange, the value of the smartphone will then be assessed by answering simple, unbiased questions on the device's condition and specifications. Once accepted, the trade-in value will be applied to a new smartphone of their choice."

Once the new trade-in program kicks off on Sept. 21, Walmart customers who apply the trade-in credit can expect to pay $98 for the iPhone 5 and $138 for the Samsung Galaxy S4 after signing a two-year contract with AT&T, Sprint or Verizon Wireless. Customers will also be able to apply trade-in credit to smartphones available on pre-paid plans such as Straight Talk.

In addition to the smartphone trade-in program, customers will also be able to trade in tablets, MP3 players, cameras, laptops, video games and more, and get the credit in the form of a Walmart gift card. They will later be able to use that gift card anywhere on Walmart's website and physical stores, but not for purchasing digital movies and TV shows.