The video above explains how to use the SMS marketing opt-out workflow. This is a great way to segment your contacts between essential texts (i.e. appointment reminders) and marketing texts.
Workflow Name: Marketing SMS Opt-in Inquiry
Message Template: SMS Opt-In
If Contact Replies No, the tag "DND SMS Marketing" will be applied.
If the Contact Does Not Reply, then the tag "DND SMS Marketing" will be applied.
When you send Marketing SMS Blasts in the future, be sure to exclude contacts with the tag.