Objective
This article explains, how you can handle anonymous incoming calls to your Twilio number and successfully forward such calls to the destination without being blocked by carriers.
As per Twilio's policy, any Programmable Voice calls where the caller ID has been withheld will now display anonymous in the From field. Refer to this changelog from May 17th, 2023: https://www.twilio.com/en-us/changelog/changes-to-withheld-caller-id-behavior
If your use case involves forwarding the anonymous call to another phone number (i.e., placing an outbound call), then the call may fail because such calls are filtered and blocked by terminating carriers.
Product
Programmable Voice
Procedure
The solution is to use your Twilio phone number as caller Id in your TwiML. A sample given below:
<?xml version="1.0" encoding="UTF-8"?>
<Response>
<Dial callerId="your_twilio_phone_number">
<Number>destination_phone_number</Number>
</Dial>
</Response>
Additional Information