It'd be really interesting to set this up over a city
Of course I know nothing about bluetooth.. but I am sure that if the phones bluetooth can't talk to you, no transfer, right? You can amplify your signal all you want but you still have to be in range to receive the handshake or whatever it is, right?
And you can only send 6 simultaneous transfers? Hell.
Also 90% of phones have bluetooth powered off, by default, right??