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.