This is possible because you are responsible for the monthly fees of the phone numbers associated with your project. Therefore, even if you are not using any of the voice or messaging services, your project may still be charged for the phone numbers you own every month.

As a reminder, you will be billed for any inbound calls or messages unless you remove the request URLs for your phone number.

If you aren't planning to use Twilio again soon, we recommend that you release any phone numbers on your project to avoid monthly charges.