Called with "Unavailable" for the caller ID. They hung up. I've disconnected my answering machine because calls like this come in all the time now. My phone has a computer voice that announces who the call is from. Seems like the phone equivalent of spam email - and at this point, just as many are coming in. I don't answer any numbers if the caller ID is not given. I am on the "do not call list." Can't block any more numbers. My phone has reached its blocked calls limit.
Also considered changing my phone number, but read that these people sell phone lists to each other so why go through the expense of that? There is no guarantee that they won't stop calling. Besides, there is also the risk that I'll get an old number that has been having this same kind of problem. Don't need to inherit somebody else's headache. Got enough of one of my own.