Earlier quoted context omitted.
Wait. Really? I had no idea this is true. You're saying there's a US law that means replying STOP is intercepted by verizon/T-mobile/etc. and the sender never has to see it?
This is not correct, I've worked with an app that had to handle SMS opt-out and we received the STOP message.
Things may have changed since, but used to work sending 8m sms messages before breakfast every day to people who subscribed to news, sports scores, etc.