On other mobile platforms (hi Windows Mobile!) we often spend quite a bit of time comparing the processors of different models, seeing which one is faster and seeing what happens when you set the clock speed of a given phone to a higher number. It's "fun," see, because not only can clock speed be radically different from phone to phone, but so can performance even on devices with similar clock speeds.
The nice thing about the iPhone: not doing that. Well, until now. MacRumors reports that the 2nd gen iPod Touch, though it sports the same processor as its siblings, actually has a clock speed of 532MHz compared to the rest at 412MHz. The result is that certain apps like TouchSports Tennis run much better on the iPod Touch 2nd Gen. Which ultimately meant that the developer had to optimize their app for the iPhone, iPhone 3G, and iPod Touch 1st Gen. All three actually perform differently with the game, with the original iPod touch falling furthest behind.
It's a bummer, because as apps become more powerful and get closer to testing the limits of the platform, developers will discover that the 'single target' advantage of the iPhone/iPod Touch platform may go away. We're not talking about having to code for as many devices as you do with Windows Mobile or BlackBerry, of course, but it's still worth noting.
Why not clock up the iPhone 3G. In a couple of words: "battery life." In a lot of words, well, battery life plus when you have WiFi, bluetooth, Quad-band edge and Tri-band WDCMA (that's GSM 3G to you) all packed together, they have to be finely tuned. Just changing the clock speed could be enough to ruin a whole raft of things beyond battery life. With smartphones, we live in a world where the choice of paint can radically alter signal strength, so it's no stretch to say the changes in heat, radiation, etc. associated with a faster clock speed could potentially cause problems. Plus, again, battery life people.
It probably wouldn't completely screw with everything if Apple upped the clock speed -- people change clock speeds all the time on WinMo -- but it can happen and it's a bigger deal as they get packed more tightly together. These radios are packed pretty tightly in the iPhone 3G.