There are certain numbers that you probably don’t want dialed with your Twilio-powered application, such as 911 or 411, which will return a specific error when dialed. This is helpful for preventing legitimate emergencies and unnecessary costs. Twilio's protection ensures that outbound applications won't be compromised by prank calls to premium paid lines. With this feature, you can confidently use phone number input form fields in your website or application without worrying about these numbers being dialed.