I receive calls frequently from 720-684-5373 which show up as "Unknown" on the Caller I.D. screen. They never leave a message, identify who they are or what they want, yet continue to call day after day. When I call the number back I get the message, "The number you have reached is not in service. This is a recording." From the 684 prefix this appears to be a telemarketing call center with an automatic redial system that is extremely persistent and annoying and needs to be stopped immediately from making further harassing calls of this kind!
I don't answer UNKNOWN NAME or unfamiliar number phone calls, so I don't know what they wanted.
What I do know is that they have called 10 times in the last five days- 7/18 through 7/24/14.
I've been on both the National as well as my State's Do-Not-Call List for years. I used to report these kinds of calls to the FCC on a regular basis. Since then, they've probably doubled in number - at least.
Another shining example of your tax dollar at work.
Calls on a daily basis up to about 4-5 times a day, just shows up on caller ID as the city of Longmont, CO, and then Lyons, CO and Aurora, CO will call within 2 minutes of the previous call