Uses a scrambled caller ID. This is a call out number (one of many in Arizona) used by telemarketers to "check" if a valid phone number exists. If it does, ie if it rings, then they copy your number into a list for auto-dialers to use in boiler rooms. Usually the number is in a remote area of the state. Once verified you start getting all sorts of political calls and so forth.

This one came up as ... D6DF6F DF6HF6F.  Sometimes these numbers are of deceased people, and other times they are Google Voice VOIP numbers, or Magicjack numbers. When they are identified as Land Line numbers they are usually spoofed. The telemarketers don't like it when you block major area codes and have to go to all sorts of trouble to find you where you went. Happens here regularly.

Once these telemarketers find out they can't call you from THEIR area code, they start calling you from your own area code to try and get through anyway. At that point you can track them easily, build up a legal case and go after them. In state phone usually companies co-operate in this way and are glad to help you go after these low-life companies.