Pretty sure it's contractual obligations by the major carriers. Traffic registration is with the carriers, not with any regulatory body. So, it's out of Twilio'

Pretty sure it's contractual obligations by the major carriers. Traffic registration is with the carriers, not with any regulatory body. So, it's out of Twilio's control but not "legal requirements". Also its technically not required for actually inbound only, but it sounds like this application also sends ack replies.