Apple appears to be ramping up the preparations for the release date of its new flagships, the iPhone 5S and possibly even the rumoured phablet-size iPhone 6, as sales promos involving old iPhone models started cropping out.

Also, fresh talents and technologies are joining the tech giant's spirited effort to deliver its 2013 device upgrades, pointing to solid indicators that major launch dates are happening soon.

Over the weekend, Apple partnered with U.S. retail giant Best Buy for a new deal that allows buyers to get $US150 price off on an iPhone 5 purchase. Customers need only to trade in their old iPhone 4 or iPhone 4S handsets to avail of the discounts.

The arrangement involves plan packages from AT&T, Sprint and Verizon so iPhone 5 buyers must verify first if they are eligible for gadget upgrades with the telco of their choice.

The deal was offered a week after Best Buy dangled the same iPhone 5 kit for only $US149, cutting down from the usual $US199 asking price that network providers slapped on new iOS smartphone releases.

These moves, analysts said, strongly suggest that Apple and its various distribution channels are prepping for the big push to come in the few months ahead - that is the unleashing of the incremental iPhone 5S bump up.

And while efforts are underway to push out old iPhone inventories, Apple is boosting its human resources pool by hiring skilled engineers, who experts said will be deployed to work on key iOS device component upgrades.

The latest to join the Cupertino-based firm are 12 former AMD employees, Apple Insider said in a new report.

These new hires along with a few more significant signals from the tech titan "set the stage for Apple to begin designing its own custom A-series processors for the iPhone, iPad, iPod touch and Apple TV," the same report said.

Apple is seen to dispatch new chip architectures via its A-series processors, which according to experts will showcase new GPU capabilities that likely resemble or exceed the prowess seen before in AMP-powered mobile devices.

Another piece of the iPhone release date puzzle is Apple's AuthenTec purchase last year. In adding the Florida-based biometrics security firm, Apple watchers are convinced that future iOS device iterations will boasts off tougher security protocols.

The upgrade will be seen first via the iPhone 5S or the iPhone 6, both of which would come with fingerprint sensors underneath the Home button, protected too by sapphire coating.

Release date for the 5S is reportedly set for September 2013 while the 4.8-inch iPhone 6 is pegged for a June 2014 debut. However, it is expected that Apple could significantly advance the scheduled rollout if only to arrest the surging momentum of its chief rival, Samsung, analysts said.

Samsung has earlier issued the Galaxy S4 and is poised to unleash its third-gen phablet, the Galaxy Note 3, also in September.