First it was Best Buy, now NextWorth lures old iPhone and iPad users to turn in their units for hefty credits on their iPhone 5 buys a few months before the rumoured September release date of the iPhone 5S.

The NextWorth trade-in promo promises effective big cuts, starting at $US100, on iPhone 5 purchases, that is if consumers would be willing to part ways with their cherished iOS smartphones and tablet computers.

The discount offer merits more than a second look but the prospect of getting into the new iPhone 5S experience, powered by the overhauled iOS 7, is more compelling according to a report by Gotta Be Mobile.

And here are the two key reasons why upgrading to the 5S a few months from now is the more prudent decision for current iPhone owners.

With iOS 7, buyers will get software and hardware bump ups in iPhone 5S

Apple is brimming with pride when presenting its completely reworked mobile platform Monday this week and it has tons of reasons to be. Chief among them are the new look and powerful features packed with iOS 7, which according to the tech giant will enhance the normal concept of smartphone - from messaging, net browsing, gaming, media playing, cam snapping and social media interacting.

It will be a whole new iPhone 5S menu, which of course will be backed by equally powerful components. It could be that the 5S profile merely represents incremental jumps but inside the unit guts lies its actual strengths - faster processor, Retina that flashes 1.5M screen pixels and cool camera features that will please shooting enthusiasts and professionals.

Apple will spring a surprise via the iPhone 5S

There has to be a giant leap on each iPhone iteration and the 5S is no different from the previous releases. With the iPhone 4, the unit was completely reengineered, while the iPhone 4S paved the way for Siri's birth. The iPhone 5, on the other and, corrected the design flaws identified such as the replacement of the glass back cover with aluminium.

In pushing out the 5S, Apple is likely to let out the perennial 'wow' factor'. Aside from the rumoured rainbow colour options, longer battery life, wireless payment via NFC and fingerprint scanner this new iPhone will unpack a mysterious but jaw-dropping ability. And being unknown at the moment only heightens the build up of excitement.

But if the reasons above are not convincing enough and the iPhone 5 seems to be gadget of choice for now, consumers will be served well to delay the purchase for a few more months and wait for the actual availability of the 5S. By that time, retail price would have dipped considerably to as low as $US99, which would be standard mark for units with 2-year contract.