Hello,
may I suggest offering an alternative way in order to collect your cash? Not everyone wants to provide his phone number and maybe someone is just there with his laptop etc. or does not want to use his phone for bitcoins.
What you could do is either ask for the phone number and do the SMS thingy in order to release the notes, or post a message that has to be signed by one of the addresses the payment came from.
The latter would obviously be more save since it cannot be intercepted the way an SMS can.
Thank you for the ideas. We will analyze them.
Nevertheless, I've from first reading some remarks:
The BTM has to be used as an entry point for bitcoins. The use of the machine is already difficult for someone who isn't aware how bitcoin wallets works. If you want on top of that use signature, only the bitcoin geek will understand. Or maybe I don't understand the point?
How do you intercept SMS? It is a very difficult task to do. The air interface between the mobile and the radio network is encrypted. As far as I know, there is no way to decrypt it on the fly.