App and game developers are preparing themselves for the launch of the iPhone 5 by testing their creations on an 'iPhone 4S' supplied by Apple.

The iPhone 4S is described as being much like the iPhone 4, but with the new A5 processor, used by the iPad 2, rather than the A4 processor the standard iPhone 4 uses, according to 9to5Mac.

Earlier this week, reports emerged that the iPhone 5 would look much like its predecessor, though would boast a faster processor.

After it was initially expected to be announced in June at the Worldwide Developer Conference in San Francisco, it is now thought that it won't be launched until September at the earliest. Some analysts think it may not even launch until 2012.

According to 9to5Mac, the iPhone 4S units don't necessarily bear any resemblance to what the iPhone 5 will look like, though.

It is thought to be in the hands of several large development agencies, though the source of the report claims that the unit they have seen spends its evenings in a company safe.

The A5 chip, based on an ARM design and used in the iPad 2, features two cores running at 1GHz versus a single 1Ghz core in the A4 processor used in the first iPad and the iPhone 4. Apple says the A5 offers twice the CPU performance and nine times the graphics power of the A4.

However, there has been some speculation that the A5 may need to be modified to be more power efficient before it can be used in the iPhone.