Seems as if there have been a few reports from the field that some iPhone 3G units cases are developing hairline cracks on their “backs.” So far, all the pictures I’ve seen show white 16GB iPhones, but it’s unusual that a black iPhone with cracks hasn’t shown up yet. We’ll keep you posted on this as we think that this is very unusual and is only happening in a very few cases. Here’s what the cracks reportedly look like: