why no facetime specific ringtone?

one can have rather granular configuration in settings > sounds, even different text tones for different persons, but no facetime specific tones, why? when someone calls, i want to know if the person is using FaceTime, so i don't inadvertently answer it when i am in a compromising position. this happened several times now i have to see what kind of call i'm getting before i answer it, even though the ringtone already tells me who is calling, this is not very productive.
i believe on the ipad or iPod, you can set facetime specific tones because it is a separate app, and i don't think it is too hard to make it configurable on the iPhone, either.