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If you’re contemplating a smartphone upgrade in the next few weeks, it’s worth holding fire for a short while.

Apple is expected to announce its new iPhone Wednesday, on 12th September and if that turns out to be the case, the chances are it will go on sale a week or so later.

The new iPhone — or ‘iPhone 5’, as many are expecting it to be called — has been the subject of the usual rumour mill for many months, but Apple has really set tongues wagging with a launch event invitation it sent out last week.

This makes no mention of a new iPhone, and only contains the numbers “5” and “12”. The event is being held on 12th September, so the “5” must refer to the iPhone 5, right? Well, no one but Apple knows, but it’s a safe bet that it’s the case.

No one really knows anything about the new iPhone either, but a succession of supposedly leaked parts mean we have a pretty good idea of what it will look like.

The most obvious change is a slightly larger screen — 4.8” across the diagonal, compared to 3.5” on the current model.

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This is expected to result in a slightly taller phone with a marginally higher screen resolution that gives a true 16:9 aspect ratio when held on its side — which has been a standard feature on Android smartphones for some time.

The other notable change is expected to be a new, much smaller, dock connector on the iPhone’s bottom edge.

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The implications of this are yet to be clear, but if true, it will mean that the iPhone 5 won’t work with any existing car kits that provide power through the dock connector. The predicted larger size of the new iPhone might conflict with some existing in-car iPhone holders, too.

It’s all speculation at this stage, of course, but we’ll provide more information following Apple’s announcement next week.

Incidentally, anyone who’s thinking of trading in their current iPhone for a new one would do well to secure a price with one of the many gadget recycling sites now.

Gadget recycling sites usually fix their price for 14 days and their offer prices for old iPhones will drop once a new model is announced.