The iPhone 6 on release date, thanks to iOS 8 and recent Apple acquisitions, is a smarter and feature-rich device, which applies for both the 4.7-inch, referred in some reports as iPhone Air, and 5.5-inch models.

Apple revealed the iOS 8 this week via the WWDC 2014 and while the software remains far from its final build, the killer features seen so far from the early beta version are expected to amaze with the two iPhone builds in the few months to come.

Also part of the welcome mix of fresh iPhone offerings are new products that Apple will likely unveil with the handsets, the company's $3 billion purchase of Beats Electronics and Beats Music and the surprise opening of banner iOS 8 features to third-party developers.

Below are the four features that likely will be unpacked with the regular-size iPhone 6 and its larger-screen sibling that analysts said will be the first Apple phablet:

iPhone 6 to pair with iWatch

Cantor Fitzgerald analyst Brian White is convinced that the rumoured iWatch is set to launch with the next iPhone. For the initial version of the Apple smartphone, it "is more of a companion device," the analyst was reported by MacRumors as saying.

While not clearly stating the specific features of the timepiece, White is under the impression that the iWatch "requires a connection to an iPhone," which he added is the main reason the two devices are rolling out at the same time.

Smart audio accessories

Apple spent billions to acquire the popular Beats Electronics but the tech giant, it seems, has grander plans for Beats and other audio accessories that will be used with iPhones and iPads. According to 9to5Mac, the company is requiring provider of iOS audio companion products to design their future products for full-connectivity with Apple's proprietary Lightning port.

The reason for the adjustment? Apple envisions playback control and other possible app manipulation through these re-engineered audio accessories, said the same 9to5Mac report.

Touch ID and PayPal

The iPhone maker is stepping on the gas for the accelerated integration of mobile payment with iPhone 6 features, which was signalled by the opening of the Touch ID API to third-party players. PayPal will be one of the early adopters, according to Apple Insider, and one proof this is the online payment processing firm has dispatch a team to attend the 2014 WWDC.

As Touch ID is expected to become a mainstay feature on all iOS devices, PayPal making use of Apple's biometrics service is seen as the start of re-inventing (anew) the mobile payment industry.

Advanced iPhone 6 messaging

The plan is to make the iPhone 6 as the ultimate messaging tool that will neutralise the emerging, sometimes even better, competition so Apple decided to pack the iOS 8 will advanced messaging functions and features.

Apple Insider listed the following as the feature upgrades to expect once the iOS 8 Messages becomes official:

- Selective notification toggle of conversations

- Timed sharing of location to specific contacts

- Message attachments preview with option to delete

- Group chats with option to label and exit the conversation thread

The above killer features are expected to make the final cut of the iPhone 6 on release date, which a new report says will be a simultaneous event on September 2014 for the 4.7-inch and 5.5-inch variants.