Will iOS 4 run on my original iPhone or iPod touch?
Unfortunately, original iPhone and iPod touch models cannot run iOS 4. In the past, Apple has made each iOS upgrade available to all previous generations of each device, but the company has deemed that the newest OS version requires too much overhead for the original iPhone and iPod touch to run it. It’s kind of like the line-in-the-sand upgrade you experience whenever Apple updates Mac OS X — sooner or later, an older Mac simply cannot run one of the major OS X upgrades because the software requires more memory or horsepower or introduces new technologies that the hardware cannot support.
