The rumblings for the supposed iPhone 5S Sept. 10 release date get stronger as U.S. telco T-Mobile announced the exit of two iPhone models from its popular handset deal catalogue.

T-Mobile, according to Apple Insider, will exclude the iPhone 5 and the iPhone 4S from its 'Zero Down' promotional campaign, which entices phone shoppers to grab the latest and previous iOS smartphone models by doing away with initial gadget payments.

While the move came as a surprise, it set off speculations that Apple's distributing partners, telcos and retailers alike, are starting to prepare for the much-awaited iPhone 5S D-Day. Apple Insider noted too in the same report that AT&T is planning to offer discounts on existing iPhone editions.

This came as AllThingsD reported over the weekend that Apple is staging an event on Sept 10, purportedly to uncloak its 2013 flagship, which many believe is the iPhone 5S, plus the reengineered iOS 7.

The Wall Street Journal tech blog site, along with other Apple watchers, also suggested that the so-called budget iPhone, alternatively known as the iPhone 5C and iPhone Lite, could also be unveiled on the same day.

These developments, experts said, are indicative of the looming 5S release date. It appears that the iPhone retail channels are prepping for the big day - either by making room for the new shipments to arrive or repackaging the old models to keep them attractive and in the process keep them moving off the shelves.

For T-Mobile in particular, the iPhone 5 costs $146 at the onset but with the expected adjustments in the aftermath of the 5S arrival, the outgoing Apple flagship handset could get a sizable price off to keep consumers coming for them.

With the affordable iPhone and the 5S assuming the lead on Apple's mobile phone line up for the second half of 2013, analysts believe that the older builds will take on new pricing points and still boost the tech giant's efforts to generate record revenues by the close of the year.

Once they become available, the iPhone 5S and its cheaper version are expected to bring in incremental updates from the iPhone 5, which analysts said should be enough for Apple to likely grab the smartphone throne back from its bitter rival, Samsung.

On release date, the 5S will show off faster processor and better Retina screen resolution plus the killer features that are embedded on the Jony Ive-redesigned iOS 7, reports said.