Have you seen these already? I think this a pretty cool way of hanging charms onto your iPhone. It gives hanging charms on your phone a whole new dimension. Since it's not possible to hang a charm on your iPhone without such a case, like you can do with any other phone.
I thought the case already looked cool without any charms (I didn't even know then, that the ring is meant for the charms), but the charms definately gives it an (Jagger) edge!