Don't have it handy at the moment, but:
Twilio IP ACL: your network's internet gateway/publicly routable IP address (whatismyipaddress.com or ipchicken.com)
I think we may have also tweaked the Public Bind Address in Ignition Voice Alarm Notification Profile advanced properties to match
(from How to setup Ignition with AWS Chime - replace ipchicken.com)