The iPad launch has confirmed that the iPhone OS is now fragmented to 2 different versions. One is for the iPod Touch/iPhone OS (v3.1.3) and the other is for the iPad (v3.2). These 2 are based on different processor chips so I assume that the back-end architecture would also be slightly different.
However, the point is whether does it make sense for them to continue fragmenting the OS. If Apple intends to fragment the OS, they could very well call it iPad OS 1.0 instead of iPhone OS 3.2. I have previously did product development for a single product that runs on 2 different databases in 2 different languages, and it's a nightmare to maintain the different branches and features. Therefore, my take is that for the sake of maintenance, the iPhone OS will not fragment.
My guess is that due to the iPad's launch date, they have rushed out the iPhone OS 3.2 specifically for the iPad, while at the same time continue adding some features to the iPhone OS for the iPhone/iPod Touch that will be launched at a later date. It doesn't really make product sense to have a iPhone OS 3.1.3 and another iPhone OS 3.2. After all, it's still quite some time till June for iPhone OS 4.0.
Coming iPhone OS 4.0, the new iPhone/iPod Touch will most probably run on the Apple A4 chip. This will allow Apple to merge the 2 branches into 1 branch for easier maintenance of the code base. Till now, there's no news of the strength of the iPad battery so I can't say for certain if it's using the same battery as the iPhone 3GS. If the iPad's battery is bigger than the iPhone, there may be some degradation of battery life for the iPhone 4G. Knowing Apple, they'll rather put a slower A4 chip in the new iPhone to lengthen the battery life if that is the case.
However, since the new iPhone OS 4.0 will be running on the new Apple A4 chip, that would also sound the death kneel for development for the iPhone 1G to iPhone 3GS. They would most probably just maintain it to rectify any security breeches. iPhone OS 3.2 may end up being the last version for iPhone 1G to iPhone 3GS.
For iPhone 4G, other than the Apple A4 processor chip, I guess wireless N should also be in the pipeline, although I seriously doubt that LTE will be in. Instead, I suspect HSDPA+ may be included to support speeds of up to 42Mbps. Contrary to whatever the Singapore telcos are saying, I do not think LTE will resolve the 3G problems that we're currently having. We're having bad connections because we do not have enough base stations. Period. The new LTE will also most probably run on the 1900 and 2100 MHZ spectrum so I doubt there'll be any improvement in signal strength.
I guess we'll know something about iPhone 4G by this Fri, Singapore time.