There are certain numbers that you probably don’t want dialed with your Twilio-powered application, such as 911 (taking time away from legitimate emergencies) or 411 (costing you money). Twilio will return a 21202 error “Phone number is a ‘premium’ number” whenever these numbers are dialed:
- (any x11 service)
Not only is this helpful for you, but it will enable you to rest assured that outbound applications where a number is specified by your end users won’t be compromised by people trying to prank or call premium paid lines (toll lines) but putting something into the input box that they shouldn’t.
So go ahead, put that phone number input form field on your website or inside your application with the confidence that Twilio will make sure your account doesn’t dial these numbers!