Dippence tipped me off on (or perhaps just promoted) these cool attachment lenses for practically any camera-phone (they attach magnetically). There's a fish-eye, and a combined wide/macro.
They look very cute/fun and even high quality, and for a surprisingly low price. Almost too low to be as good quality as they seem, but heck, fun is fun.
One should note that such lenses of course does not replace the phone's existing lens, it modifies it. This means that the end result can't be quite as high quality optically as the lens on its own, but then with today's optics it does not need to be very much lower either.
The reason is that lenses are very precise and complex, and if you add something to a lens, it has to be painstakingly attuned to and produced for exactly that lens to not reduce the quality. Nikon for example has a zoom lens and tele lens with dedicated teleconverters which deliver virtually the same quality as the naked lenses, but this is an unusual achievement.