it doesnt work well on my phone - as tom hinted it will depend on your phone/camera. i worked the method out before i bought the trick and liked the idea, but knew it could have some drawbacks, it could work well on some phones, but not mine!
i think linda has a good point, it is very easy to do with software and so not that amazing for some people, when i tried calling card on a friend he instantly sussed the method and i only gave him a very quick 'flash' of the pic.
i would like to see this on other phones, to see if the effect works better as i think the idea is cute, but not as amazing as the ad blurb makes out.
could someone please tell me what CUPS means - i think i suffer from this disease very badly and would like to know its full name so that i may start on the road to recovery