Could Twilio simply add a boolean to their 'make a call' API endpoint where the user has to declare that they have, in fact, obtained consent to call a particular number?
That would provide no technical barrier against fraud, but it may suffice as a legal CYA for Twilio.
Actual FCC C&D letter is at https://www.fcc.gov/document/fcc-issues-robocall-cease-and-d...
Key takeaway, there is no safe harbor CYA of the type you suggest, they need (and basically immediately) to take effective steps to prevent robocalls that are factually illegal, they don't have the option of getting CYA certificates from their users to insulate them if the users keep making illegal calls.
While I'm certainly far from being a contract lawyer, it looks to me like the FCC is interested in receiving evidence of consent for the offending calls, if it exists:
>The Traceback Consortium conducted tracebacks and determined that Twilio was originating apparently unlawful robocalls on behalf of MV Realty through its dialing provider PhoneBurner. The Traceback Consortium notified Twilio of these calls and provided access to supporting data identifying each call, as indicated in Attachment A. Twilio told the Traceback Consortium that PhoneBurner had obtained called parties’ consent for the robocalls. Neither Twilio nor PhoneBurner provided the Traceback Consortium with evidence of consent.
And:
>If Twilio has evidence that the transmissions identified in Attachment A were legal calls, present that evidence to the Commission and the Traceback Consortium.
In any event, if consent to place calls is required, then there has to be some mechanism for call origination services (here, Twilio) to demonstrate receipt of that consent. My question is, what exactly does the FCC require as proof of consent?