I think it would be in VAPI's best interest to build their own. in-house. Something versatile, like a script for a (customizable via CSS) preliminary input form that: A) Makes them demonstrate control over the phone/phone number. B) Captures the phone number C) Captures their explicit consent D) Captures their IP Then it adds it to a database that VAPI has control over. When they opt out, they're removed. Only numbers that have given consent can have calls placed to them.