Whitelisted Challenge/Response Proposal

The telecom providers create a whitelist for each subscriber. Subscribers can manually add to the whitelist via an online interface (website provided by the telecom providing company). If a caller is not on the subscriber's whitelist, they will have to enter a code (the code will be verbal and the caller will have to key in the corresponding numberic response or could use IVR). Once the call goes through, the subscriber will receive the call followed by the option to add that number to their whitelist.