It's a CorCom dial up service provider number, no calls are supposed to be going out on it. The criminals that our government lets run free jack these numbers ( spoofing) and that's why when you call it back you get the signal that sounds similar to a fax machine tone set- it thinks you are a computer and expects you to converse in digital. But, you are not contacting the REAL criminals that called you. The phone companies could put a stop to this harassment but there is to much money to be made. Blocking does no good, they will just pick another number to harass you on tomorrow. Probably "Card Services", the usual anal warts that plague society....