iPhone 4S (fifth generation)

Launched: October 2011

iPhone 4S
Siri made its debut with the iPhone 4S, which also featured an improved camera.

Apple pulled out the "S" tag again for the fifth generation handset, indicating a minor upgrade rather than a major overhaul.

The design of the iPhone 4S was the same, but inside was Apple's new A5 processor, vastly improved graphics capabilities and an 8MP camera with 1080p video recording. iOS was evolving at the same rate as the hardware, of course, and Siri began life as an iPhone 4S exclusive.

The improvements were enough to persuade us to describe it as "the best thing Apple has ever created" in the official TechRadar review.

iPhone 5 (sixth generation)

Launched: September 2012

iPhone 5

Six handsets later, Apple finally decided it was time to tweak the iPhone's screen size and aspect ratio.

Coming in at 20% lighter than its predecessor, the 2012 iPhone adopted a 4-inch screen running at 640 x 1136 pixels.

Otherwise, despite the usual speed bump and a stronger antenna, it was very much business as usual in terms of the design and capabilities.

Our biggest gripe in our iPhone 5 review was with the aging iOS, but with iOS 7 arriving on September 18 that issue is very much negated, which will please a number of iPhone 5 users who've been holding onto the handset for nearly a year.

iPhone 5S/5C (seventh generation)

Launched: September 2013

iPhone 5S

The big step in the seventh stage of the iPhone's evolution was the arrival of the iPhone 5C, a slightly cheaper, plastic-backed model to help battle Android in the busy mobile middle market. The signs were there already — remember Apple kept the iPhone 4 and 4S on sale during the iPhone 5 era.

Apart from the plastic shell and larger battery though the iPhone 5C was a carbon copy of the iPhone 5 in terms of specs - which was retired to make way for the two new handsets.

As for the flagship iPhone 5S, it was a case of under-the-hood improvements again: more power, a better camera, and a fancy fingerprint reader hidden under the home button. The bigger changes arrived with iOS 7, the most radical revamp of the mobile operating system since the App Store arrived back in 2008.

iPhone 6/6L

Launching: September 2014

iPhone 6

Which brings us to now, the eve of the next Apple handset - or should that be handsets?

We're at that familiar point in the cycle where it feels like everything about the next iPhone has been leaked. The standard iPhone 6 is expected to come with a 4.7-inch display packing a 1334x750 resolution, which may come built from scratch-resistant sapphire.

But it's the new design that we're most intrigued by: if the leaks are to be believed then the iPhone 6 will be slimmer with curved edges, while the power button has been moved from the top to the side of the handset.

Inside we're betting on a new 64-bit Apple A8 processor, a better motion co-processor, either 1 or 2 GB of RAM, and possibly storage options up to 128GB.

When it comes to the camera things are a little less certain: some people claim that Apple's sticking with an 8MP snapper, while others claim it's bumping up to 13MP. We'd say the latter is more likely.

Meanwhile a bigger handset, arriving with a behemoth 5.5-inch display, is believed to be arriving hand in hand with the smaller sibling. The specs may be given a slight boost, they might not. What we have heard, however, is that the big iPhone will offer a one-handed mode for easier use, and may even take some interface cues from the iPad.

We're currently referring to it as the iPhone 6L as that's what Apple is rumoured to be calling it, but its final moniker could be just about anything. Place your bets now.