According to reporter Nobuyuki Hayashi, the camera of the iPhone 3G sold in Japan will make a shutter sound every time you take a photo, even if you put the telephone in silent mode. The reason: all those pervs taking photos up the skirts of unsuspected women in public places.
According to Hayahi, the problem of up-skirt photography is so bad in Japan that most new mobile phones have this feature (if you are a women) or bug (if you are a perv.) According to him, "some manufacturers have even put a louder shutter sound." The Japanese edition of the iPhone, however, just makes the normal one.
I really don't see the point of this measure however: the iPhone doesn't have a physical photo button, which really makes extremely difficult to take a clear up-skirt shot.
I mean, I can only guess that's the case.
Two things to Japanese pervs everywhere: fibre optics and video cameras.
Update: as readers have noticed, you can use Pwnage to jailbreak your iPhone and remove the sound. Why would you want to do this, I don't know.