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Best Buy offering 'free' iPhone 5 in its trade-in promotion

The tech retailer is doing it again -- customers now have nine days in which they can trade in a working iPhone 4S or 4 and get a $150 credit for a new iPhone.

Apple's iPhone 5.

After Best Buy hosted an iPhone trade-in day earlier this month, the retailer has decided to do it again -- but this time, the deal will last for nine days.

The way the program works is that customers can bring in an iPhone 4S or 4 and trade it for a brand new iPhone 5, according to USA Today. Between June 21 and June 29, Best Buy will give customers a $150 trade-in credit for their old phone, which makes the iPhone 5 free (the 16GB iPhone 5 currently costs $149.99 at Best Buy with a $50 instant rebate).

The only out-of-pocket costs for the customer will be any applicable sales tax on the new phone and any applicable carrier activation fees. Customers must be eligible for an upgrade and activate the iPhone 5 on a two-year contract with Verizon, AT&T, or Sprint to take advantage of the offer. Also, the deal isn't available online -- customers have to go to Best Buy's retail stores.

The tech retailer did the exact same iPhone trade-in program on June 1 and apparently it was successful. According to USA Today, Best Buy said it was its biggest day ever for the trade-in program, which has gone on for the last four years.

The move by Best Buy comes as the retailer boosts its focus on mobile devices and other tech gadgets. Besides matching online pricing for the devices it sells, Best Buy also plans to feature more partners' products, such as the Samsung mini shops that just opened within all Best Buy stores.