I'd say the novelty of it is enough of an incentive for such an idea. Also, bumping two phones together carries lower psychological cost than handing someone yo

I'd say the novelty of it is enough of an incentive for such an idea. Also, bumping two phones together carries lower psychological cost than handing someone your hard-earned cash and I would expect people to have less qualms about lending/returning/trading small sums of money this way.