Best Buy has concocted quite the offer in an effort to lure would-be iPhone 5S and iPhone 5C buyers to its blue-and-yellow storefronts.

With the trade-in of any working phone, the retailer will guarantee at least $100 credit towards a new handset. Since the 16GB iPhone 5C costs $99, customers are basically getting a free phone, though they are subject to sales tax and activation charges.

A basic iPhone 5S would cost a bargain-bin $99.

The retailer confirmed the deal to AllThingsD, noting that customers can take advantage of the iPhone 5C offer at Best Buy Mobile stores starting today. Beginning Oct. 13, the promotion kicks into full gear. It all ends Oct. 19, so time is of the essence.

The biggest catch is that customers must be eligible for an upgrade, so don't go sauntering into a store looking for a free phone if you just bought one. Nice try though.

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