My iPhone 3G which is a 16GB version can upgrade to newer iOS in the past, but for merely 2GB of total usage on this iPhone, iTunes will take an hour or more to "Back up the data".
I know that some slow flash memory may take 2MB/second for data transfer, but even at that speed, 500 seconds should be good for 1GB of data, and 1,000 seconds will be good for 2GB of data, so that should be 16.67 minutes only. (and, 2MB/s is usually a bottleneck speed for data writing, not for reading. The speed for slow flash memory read that I usually see is 6MB/s)
Is it a design issue or might there be even a product recall for this issue? If the iPhone 3G is taken to the Apple Store's Genius Bar, will they be able to swap another phone that takes a lot shorter time? (My iPhone 4 and 4S, for example, is a lot faster for backing up the data when upgrading iOS).