The 571 area code is used pretty much all over Northern VA. This particular number shows an address of Ashburn, VA, which is in Loudoun County. And I think you're right that it's also used for some land line phones now (in addition to cell phones) and, since reverse lookup shows a name and address, I think this one is most likely a land line. Also because a name and address is available, I have a feeling that this is some small business doing their own telemarketing. They have a tendency to believe that they can ignore the do-not-call registry or that the FTC won't do anything about it, and they may be right. I've had the same problem with a small business in Fredericksburg (Rayne something) that offers free water testing as a lead-in to try to sell water softeners. I've reported them countless times but they still keep calling. I'm beginning to wonder what good the DNC registry even does.
I got a call from this number, they hung up, left no message. I called them back and got a recording that this number has not been assigned yet. It's obviously a telemarketer call or a scam. I will report the number and then re register all my numbers on the DNC - for what little good that will do. I'm on there already!