Protecting you from Nasty Numbers

A customer wrote today with a great question:

Q: “Does twilio protect me from placing calls to nasty phone numbers that may be entered by an end-user, such as 911?”
A: Yes!

We do indeed protect you from abusive uses, so you can feel free to pass-through to use whatever phone number a user enters. Here’s a list of restricted phone numbers that will be returned as an error:
911
411
(any x11 service)
(XXX)-555-1212
900/976
If one of those numbers is submitted, we’ll return an error code 21202 (Phone number is a ‘premium’ number).