<Hangup> verb ends a call. If used as the first verb in a TwiML response
it does not prevent Twilio from answering the call and billing your
account. The only way to not answer a call and prevent billing is to use the
<Hangup> verb has no attributes.
You can't nest any verbs within
<Hangup> and you can't nest
<Hangup> within any other verbs.
The following code tells Twilio to answer the call and hang up immediately.
- When receiving a Twilio request to an 'action' URL within
<Sms>, you can return a response containing the
<Hangup>verb to end the current call.