OptionalAsyncEnables asynchronous answering-machine detection: Twilio keeps the call flowing (so the agent can
start speaking) and later POSTs the verdict (AnsweredBy) to AsyncAmdStatusCallback. Maps to
machineDetection: 'Enable' + asyncAmd: 'true'.
OptionalAsyncURL Twilio POSTs the async-AMD verdict to. Maps to asyncAmdStatusCallback. Required when AsyncAmd is set.
Originating caller-id / DID. Maps to Twilio's from.
OptionalStatusOptional status-callback URL for lifecycle events. Maps to Twilio's statusCallback.
OptionalStatusLifecycle events to post to StatusCallback (initiated/ringing/answered/completed). Maps to statusCallbackEvent.
Destination number (E.164). Maps to Twilio's to.
The TwiML executed when the call connects (our <Connect><Stream>). Maps to Twilio's twiml.
The REST payload ITwilioRestLike.calls.create accepts (the subset we use).