Number was on my Caller ID, but no message was left.  When I called back, I got a stilted automated recording which told me that I was called by a number used for surveys and which was therefore exempt from DNC.  The voice apologized for any inconvenience, read back my number, and said that I'd never be called again by the survey.  We'll see whether this promise is kept, but since no one before me reported this number, I'm optimistic.