I'm faced with the same issue.
From what I understand, BYOC means that you can point another carrier's numbers at Twilio without having to port them to Twilio. However, BYOC on Twilio does not seem to have any way (that I can see) to set up a number within their portal that another carrier owns.
Within the VAPI dashboard, I cannot import the number because it does not exist within the Twilio Phone Numbers. We would need a way of adding these numbers we have via BYOC.
We have BYOC set up and working correctly within Twilio, and we can see the inbound call in the Twilio logs, which sends the call to VAPI.
How do we set this up in VAPI or Twillio?