Best Buy is giving consumers a solid reason not to wait out until Christmas time to snap up the newly-released iPhone 5S for only $100 and its plastic-wrapped sibling, the iPhone 5C, for free.

The giant retailer dangles a $100 discount for a limited amount of time.

Shoppers, according to Techno Buffalo, only need to hand in their working smartphone, any brand, to take advantage of the 7-day promo that kicks off on October 13, a Sunday. Deal seekers are advised to hurry as the offer expires on the 19th of the same month.

But there is one key reminder for would-be swappers, the same report said. They need to ensure that not only the device they're handing in still breathe but also the toys remain sellable minus the need for a makeover.

That means cracked screens are out of the question and handsets that have been soaked and damaged by water - these goods are definitely deal breakers.

Citing an internal Best Buy document that was provided by an anonymous insider, Techno Buffalo stated that like in usual promos from the likes of Walmart, Target and Amazon, the gift card are for exclusive in purchasing the iPhone 5S and 5C.

Also, a 2-year lock-in period comes with the package, which suggests that the U.S retailer is working in partnership with major American telcos.

Obviously, consumers will need to visit a Best Buy branch to get hold of the trade in deal, which easily presses down the 5S sticker to only $100 and the 5C a take home without plunking down any cash.

According to Apple Insider, the new promo cannot be combined to Best Buy's existing marketing push for the iPhone 5C, which is currently up for grabs for only $50.

It appears too that not all Best Buy are participating in the promotional campaign so it is best to check first before heading out, the same report said.

The swapping offer came up as other retailers push out a frenzy of deals that mostly involve the 5C, which according to recent reports are not moving off the shelves as expected by Apple.

Analysts are expecting more price cuts to come involving the mid-range iPhone as the months of November and December approach.

Yet it is a different story for the iPhone 5S, which according to Apple has exceeded the record sales numbers posted by the iPhone 5 when it rolled out in late 2012.

For sure, Apple's retail partners and distributors will wrap the 5S in attractive price deals in the months ahead but the upcoming Best Buy promo could prove as lowest price point ever for the iOS 7-powered smartphone, analysts said.