My guess would be that he's looking for something similar to what you can get through Qwest.

i.e. If the phone number is blocked, it plays you a recording that gives you the option to type in your phone number or hang up.

I have this on my home phone, and I love it. Most telemarketer types won't take the time to put in a phone number.

Here is an example of why this might be a good idea:

When my husband calls me from his cell phone while he is roaming, the caller id says "UNKNOWN." If he calls the house, he just types in the last four digits of his phone number and I know it is him.

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Nicky