I've been receiving spoofed-numbered calls for months, many of them would come in as "Customer Service". They would always ring 3 times and hang up. I started keeping a list an the list grew to a couple of pages of random numbers, many of them ID'd as "Out of Area". Some with my area code would show up as "Out of Area" (and a bogus prefix that started with a "1"). Always 3 rings, never a message. So I began to piece together that my number was on an "auto-dialer" list and I was getting dozens of calls from "bogusly" ID'd numbers.
My friend gave me the best advice I could ask for. Here it is:
Go find the recording (it's posted on the web) of "The number you have reached is either out of service or disconnect...". I have an old digital answering machine. I played that recording, through my computer speakers into the answering machine as my "Outgoing Message". Leaving the volume up, when these bogus auto-dialer calls came in, I answered my phone on speaker phone, held it up to the digital answering machine and played the outgoing message - "The # you've reached..." I played it twice til I could determine I had a dead line. Within a minute, the auto-dialer called again to check to see if the number was really disconnected. I played the outgoing message again twice. SInce then, my phone has gone completely SILENT of these auto dialer calls.
Try it if you like. If you're getting a lot of them, figure out through your caller ID which ones seem to be the auto-dialers and then let them have the message. Be prepared to play it again when they call right back. Good luck.