Maybe a change to Caller ID:
If the caller ID matches the ANI, send it on through. If it doesn't, put a star in front of the caller ID. Then have an option for blocking any starred numbers, or doing a Captcha.
If the caller ID matches the ANI, send it on through. If it doesn't, put a star in front of the caller ID. Then have an option for blocking any starred numbers, or doing a Captcha.