On second thoughts.....
This is what I've always wanted, cos every time i go off on holiday, I always bring a little slab of polished granite with me in my case, just for this very purpose.... lol
It might work i suppose if you set it in the middle of your car roof, then watch it vibrate off down the other side onto the concrete before you manage to catch it... Ooops... lol
Good idea tho, but not practical in practice.. Unless your in a room taking a photo with it on a desk or something..
I was going to buy it anyway for its novelty value, but the first 5 reviews or so all gave 1 star, and said it doesn't work and their phone doesn't move..
Maybe a little squirt of WD40 under the phone might help? KY Jelly anyone? lol....