Do I need to purchase a Twilio number if I only want to place outbound calls?
No. You’re able to verify non-Twilio phone numbers and use them to initiate outbound calls via our REST API. You are not obligated to use a Twilio number, however, if you want to be able to receive inbound calls you will need to have a Twilio number configured with a Voice Request URL.
To learn about the number verification process, please refer to this FAQ article.