The speculation is flying that Apple will take the wraps off the iPhone 5 in September to coincide with the release of the latest version of its iOS operating system for mobile devices following a report in The Wall Street Journal this week.

The Journal, citing sources in Taiwan, where key suppliers to the company are headquartered, reckons Apple has a target of shipping 25m units of its next device by the end of the year and that initial production will be “a few million units”. The newspaper’s sources also say Apple wanted to start shipping the new iPhone in the southern hemisphere winter but wasn’t able to because of supply constraints.

What should consumers expect from the next-generation device? First of all, it’s still not clear what it will be called. Reports have suggested it will be called the iPhone 5 or the iPhone 4S. If it’s the latter, it suggests Apple’s next phone could be an incremental update rather than representing a big overhaul.

What is likely is that the iPhone 4S/5 will be both thinner and lighter than its predecessor — no surprises there — and come equipped with an 8-megapixel rear-facing camera. That’ll keep it in contention next to rival Android-based handsets like Samsung’s new Galaxy S II and the HTC Sensation.

In terms of the actual design of the handset, some rumours suggest a complete overhaul of the iPhone 4, while others point to minor changes such as the addition of an LED flash (or even two) for the rear camera and a thinner bezel, with big changes only coming with the model after next, sometime in 2012.

Others anticipate drastic changes like a larger bezel with capacitive buttons or even two different models of iPhone 5, one a premium device and the other a cheaper, less feature-rich one.

What a next-generation iPhone is likely to sport is a dual-core processor, possibly the same A5 chip that powers the iPad 2. It may also include support for near-field communication (NFC) technology, which allows users to make payments by touching their device to an NFC-enabled pay point.

The Journal also quotes an unnamed source hinting that the next iPhone could include some sort of new charging technology. This has led to speculation that Apple could be planning some sort of wireless induction charging system, or that it’s finally abandoning its proprietary connector in favour of the universal micro USB standard (but don’t count on that).

Of course, we already know the next-generation iPhone will support integration with Apple’s iCloud.

Since the first iPhone was introduced in 2007, Apple has sold more than 100m of the devices. In the first quarter of 2011, the company sold nearly 19m iPhones. — Staff reporter, TechCentral