Old and current iPhone models are getting a $US50 price cut via Best Buy beginning this week, further fuelling speculations that Apple soon release the upcoming iPhone 5S and even the rumoured iPhone 6.

The sales promo was started by the U.S. retail giant on Sunday, affecting all the iPhone 5 models and the 16GB iPhone 4S, according to Apple Insider.

Best Buy is offering the handsets with the direct collaboration of three major U.S. telcos, AT&T, Sprint and Verizon, so consumers will have two accept the full gadget packages that normally come with a plan contract that lasts two years.

By virtue of the sales initiative, the iPhone 4S' price tag is now down to $US49 and buyers will be taking home the sole model that Apple still sells - the 16GB.

Those opting for the iPhone 5 will have to pay a slightly higher price - $US149 specifically for the 16GB variant that normally is up for grabs at $US199. The 32GB and 64GB are on the table too for $US249 and $349 respectively.

According to Best Buy, these price levels will be in effect for four weeks, ending by mid-June, which is a period pegged by analysts as the ramped moment in Apple's production lines for the next iPhone iteration.

Retailers and distributors usually accelerate their efforts to lure more buys on existing gadget models to maximise revenues and to clear out inventories in preparation for the arrival of fresher models, which in Apple's case is the iPhone 5S.

Touted by analysts as representing incremental upgrades, the new iOS smartphone is believed to deliver only a few killer features such as a fingerprint sensor embedded underneath the sapphire-coated Home button, a 12MP shooter, a revised iOS 7 with a prominent black and white look plus new phone housing colour options.

The earliest release date set for the 5S is September 2013.

The phablet-size iPhone 6, on the other hand, will come next year, likely on June 2014 and Apple watchers are anticipating a major remake of the device. Highly anticipated specs are a 4.8-inch wrap-around screen and disappearing or capacitive control keys, including the iconic Home button.