Called, claiming to represent a "Duct cleaning and air conditioning inspection company" in Silver Spring, Maryland.  Reminded the caller that he was violating the "Do Not Call" prohibition for contacting telephones which are listed (as my phone is) the DNC registry.  Caller insisted he "had a license to make such calls," and argued with me, telling me I was wrong.  I then hung up.  Caller seemed to be from either India or Pakistan, based on his accent.