Retailer Best Buy is set to kick off a fantastic deal for the recently launched iPhone 5s and iPhone 5c.

Come Sunday, October 13,Best Buy will kick off a trade-in promotion where it will offer a gift card of minimum $100 in exchange for any working smartphone. However, there is a catch as this gift card can only be used towards the purchase of the latest iPhone 5s or its cheaper sibling the iPhone 5c on a two-year contract. The Best Buy trade-in offer is a limited period one and will be valid till Saturday, October 19.

This information was first reported by TechnoBuffalo, which managed to lay its hands on an internal document thanks to "trusted sources."

"A trusted source has provided us with a screenshot of an internal Best Buy document that states the retailer will be running a promotion from Oct. 13 to Oct. 19 that will allow you to trade-in select smartphones and receive a minimum of $100 in credit," notes TechnoBuffalo.

When contacted by Mashable, Best Buy confirmed the upcoming promotion and let on that it would run the trade-in offer for a week.

"The offer runs from Oct. 13 to Oct. 19 and is good for customers who trade in any working smartphone," the company said in a statement. "If a customer's smartphone is worth more than the guaranteed credit, they will receive the positive difference in the form of a Best Buy gift card."

This offer, however, cannot be clubbed with the existing Best Buy Promotion for the iPhone 5c, whereby one can purchase the handset for $49 with the $50 Best Buy gift card.

To qualify for the Best Buy offer, the smartphone being traded must be in working condition and undamaged i.e. no cracked screens or water damage. Those taking advantage of the trade-in offer would be required to sign-up for a two-year contract with a supported carrier for either the iPhone 5c or iPhone 5s.

Additionally, customers who bring the smartphone they are looking to trade, in the original packaging, and/or with original accessories, could see the trade-in value increase.

This trade-in offer is valid in-store only; however, not all Best Buy locations may qualify for this trade-in offer, per the internal document. Therefore, it is advisable to call your local Best Buy store ahead and to check if they have the trade-in offer going on.