Carriers and SMS service providers (like Twillio) obey that, no matter what service is behind. There are stories of people replying STOP to spam, then never ge

Carriers and SMS service providers (like Twillio) obey that, no matter what service is behind. There are stories of people replying STOP to spam, then never getting a legit SMS because the number was re-used by another service. That's because it's being blocked between the spammer and the phone.