This post a response to The Next iPhone on Sliceofmymind.com.
First of all, you've got it all wrong. The upgrade from 3G to 3GS was significant. The processor speed and graphic performance were improved to the point where iPhone 2G/3G were practically (with the older hardware) were slow as hell, and a gigantic pain in the ass to use!
Processor is 600MHz up from 412MHz, with a dramatically improved GPU, and double the RAM, 256MB up from 128MB. Digital compass for directional uses, dramatically improved 3.2MP camera with tap-to-focus, video capability, improved battery life, etc. The list just goes on! So don't even go blabbering that 3G to 3GS was a "minor" upgrade.
Now, speaking of the iPhone 4, and if Apple released an iPhone 4S, it wouldn't be a "minor" update. After all, the A5 processor that the iPad 2 sports is about 2.5x more powerful than the Samsung Galaxy S II, which currently has the one of the most powerful guts of all available phones, and if that's not pretty damn good to you, I don't know what is.
Overall performance wise (software AND hardware), the iPhone 4 to this day even outperforms MOST new phones that come out, and that says something about what putting a simple little A5 inside an iPhone would do, whether or not Apple redesigns the external hardware. We'll all just have to wait and see!