Rec'd call from 1-576-898-6593 at 2:30 pm 10/26/13.  Caller ID "Name Unavailable".  Didn't answer and no message was left on answering machine.
Checked and 576 is not a valid area code.  "Any area code listed as an unassigned area code is an invalid area code when it was last checked. If you're receiving a call from an unassigned area code, it is likely a telemarketer is spoofing the phone number, making it appear as if they are someone else and so the call is not blocked."
(from:  http://www.computerhope.com/areacode.htm#spoof)