They're not toll numbers. They're regular numbers. Mobile networks get paid a small amount of money for delivering SMS messages. Let's say that they get paid $0

They're not toll numbers. They're regular numbers. Mobile networks get paid a small amount of money for delivering SMS messages. Let's say that they get paid $0.003/message. Let's say you're a small mobile network and I bribe you or make a deal with you: I'll get lots of messages sent to mobile devices on your network and you'll pay me $0.001/message. That's good for you as the mobile network and good for me since I get money. So I get a list of numbers on your network and start filling them into any form that will send a text to that number. There is no "don't send messages to scammer toll numbers" option because these aren't toll numbers. They're regular numbers. I mean, Twilio could probably easily detect this behavior themselves and prevent it. As they note, they often cycle through adjacent numbers and do it in a quick fashion. However, the numbers aren't scam/toll numbers as a category. You'd need to use ML/heuristics to find these.