Since the iPhone 4S was cosmetically near-identical to the iPhone 4, expect a wholly new design this time around. Leaked images suggest a similar glass front but with a proportionally longer display: enough for an extra row of app icons, which may cause app developers some headaches or mean that older apps have black lines at either edge, working as they always used to. The longer screen could make video watching more pleasurable as it'll be closer to the widescreen 16 x 9 ratio.
Rear metal jacket
It will also have a metal back. Since it's hard to get signals (wi-fi, 3G and so on) through metal, expect a section that's more signal-friendly like glass or plastic. The first iPhone had a plastic section on the back for this purpose.
And along with 3G, expect the new iPhone to have 4G, too. Of course, at first there'll only be one 4G frequency in the UK, the 1800MHz band chosen by Everything Everywhere and theoretically switched on tomorrow. There's no confirmation but I'd say that this frequency will be included in the iPhone 5, making it a poster boy for speedy data transfer. At last, no more stuttering browsers or long delays for web pages to load. Yeah, right.
A bigger screen
This is the development that's as near-definite as can be. Last year, rumour has it, a bigger-screened iPhone was on the cards but was nixed when the apps just didn't look good enough. So if that problem's solved, expect a 4-inch display, instead of the 3.5-inch one all previous iPhones have had. It'll still be a Retina Display, though the resolution will change to fit the larger display.
That display may well use a different technology that makes it thinner, allowing the iPhone 5 to slim down overall. Not that the current model is plump, but the new one may shave around 1mm off the thickness.
The latest OS, version 6, will be on board with gorgeous new maps (courtesy of TomTom) and improved capabilities from Siri, the voice recognition program. Note that some of the Siri features may only be available in the US at first.
Your dock connector won't fit
The familiar 31-pin connector on the base of the phone is likely to be replaced with a smaller one - though not the microUSB connection on almost every other handset. So your iPod speakers will need to be replaced or to have an adaptor to work.
The iPhone 4S processor is called the A5; the latest iPad has the A5X, which is the A5 with extra graphical processing grunt. Expect the A5X or even a new model called the A6 to feature in the iPhone 5.
The new software includes a neat feature called Passbook which will collect together your boarding passes, tickets and more. It may be connected to the phone's GPS, so your plane ticket could pop up on screen as you approach the airport. And it could feature NFC, the contactless connection used in the London Oyster card system. NFC is already on several mobile phones but Apple could be the first with an end-to-end system to make NFC really work, though again it may only be for the US at first.
A bigger battery, smaller sim
That 4G drains battery life faster, so it's likely there'll be a bigger cell in the iPhone 5. And since Apple likes to make other components smaller to allow for more battery, expect the rumours of a nano sim to be true. Apple switched from a regular sim card to a micro sim with the iPhone 4 and now nearly every high-end phone favours the smaller model. A similar rush to the smallest sim may follow from other manufacturers.
Overall, the new iPhone is likely to be a much bigger upgrade than from iPhone 4 to 4S. And though many fanboys will be disappointed, you can expect it to sell in greater numbers even than its super-selling predecessors.
So, when can I get one?
Apple always releases within days of its product announcements. The only exceptions are for the first of a new type of product, when approval from the American FCC is required in advance, which is why the first iPhone and iPad were announced months ahead of release. That doesn't apply here. Apple likes a big opening weekend and favours Fridays for onsale dates, so you can bet that the iPhone 5 will be in stores on Friday 21 September, with pre-orders probably starting on Wednesday. On your marks...
The images on this page are mock-ups of how the iPhone 5 *may* look by designer Frederico Ciccarese
On MSN Tech & Gadgets: Apple iPhone 5: what we know so far