Walmart is following Best Buy, Apple, Gamestop, and the rest with a trade-in program that offers up to $300 in-store credit for your old smartphone. From September 21st, Walmart customers at around 3,600 participating stores will be able to receive immediate credit for their old phone and put that against the purchase of a new one. "Credit" is the operative word here — you're not getting cash for your phone, and the credit can only be redeemed against on-contract and prepaid handsets. Although there's no comprehensive list available yet, Walmart says it'll offer $300 for an iPhone 5, $175 for a Samsung Galaxy S III, and $52 for a Samsung Galaxy S II.

Those prices — especially the iPhone 5, which is capped at the maximum $300 — may seem a little low when compared to competitors like Amazon and Gamestop, but it's worth noting that September 21st is the day after Apple's new iPhone 5S is rumored to be released. The launch of a new high-end iPhone will obviously have a knock-on effect on the rest of Apple's range, and makes Walmart's promise of $300 not a terrible deal.

Of course, the best option if you're looking to trade in your smartphone is to compare the prices at a number of stores, and 9to5Mac recently looked at how Apple's trade-in program compares to a number of retailers, so if you're in the mood for a new iPhone that's a good place to start. Even if others offer improved rates, Walmart will likely see traction with its new scheme thanks to the convenience of being able to trade your phone in such a popular store.