Twilio phone numbers may be called or texted to by outside users, just like any other phone number. To help ensure against calls and messages that aren’t intended for you, we wait for a minimum of two months before recycling phone numbers, so that the former owner can update their records. In addition, we monitor each reserved number until it reaches an acceptably low number of contacts.
That said, some customers may still see unwanted contacts on their Twilio number. If you experience these issues, here are some tips:
Unwanted incoming calls to your Twilio number can be blocked in a number of ways: Using a blank webhook, responding with the <Reject> verb, or even a "virtual blacklist". Full details can be found in our article How Can I Stop Receiving or Block Phone Calls?
To prevent all incoming messages and corresponding charges, remove the webhook URL from your Twilio phone number. More details can be found in our article Is there a way to block incoming SMS on my Twilio phone number?