I have been getting phone calls anywhere from 1 to 8 per day from numbers originating in ALL the area codes in Virginia for about 3 months now... I block them ( I can block up to 5 on my cell carrier) and it stops for awhile... then it crops up with a whole new set of numbers from Virginia. When I answer no one is ever there... half the time the phone barely rings once and the call cancels out. Never once spoken with anyone... sometimes I pick up and say nothing so there is "nothing" to pick up on.. or I open then close my phone.  It's annoying but since I have caller ID I just don't answer it if I don't want to.

  Yeah, it is frustrating. Still, if you use the Internet (and everyone who reads this does), you can clearly see from a couple posts what is what. After a while, you get one hell of an education:
  Offshore callers "spoofing" Caller ID, boiler room collectors using lame techniques to collect debts that are not related to you at all, collectors using callback techniques that run just this side of breaking the law, telemarketers or collectors bouncing their number off another number to hide their identity....TONS of scammers and scumbags, yes.
  'Old, but not brain dead' makes good points, as do many posters about these types of calls.
Let me add:
-If you make the mistake of answering, you might well have added yourself to many more lists; often a robo-call is getting information on when a live human is answering and will then sell your number to hundreds more scumsters
-Obviously, you don't really need to call back to get your info; Googling is what got most of these commenters here...I thank Goodness for these pages and threads. They've saved (and continue to save) me from getting added to even more call-lists
-Don't assume that the DNC List will stop these calls; many have no problem breaking the law; there's also some evidence, from these very threads, that adding yourself to the DNC List will actually increase these calls
-Many will tell you this simple statement; perhaps it's time to consider it: "If they don't leave a message, how important is it?"

I could go on, but if you do your homework by reading every thread you can about these callers, you will eventually get pretty good at both ignoring the calls, and not getting worked up about them either. It happened to me.