I don't know who it is either. They called my cell just now and didn't say anything when I answered. I checked on White Pages and saw that some people reported it as spam about winning a trip.
This number, 301-859-3167 has called my cell phone several times already and no VM was left. Number was blocked permanently on the first call.
I goggled this number and the only thing i can find out, provided that the number hasnt been spoofed, is that it belongs to a company called "Green Study Survey Company" located in Oxon Hill Maryland.
Not sure what type of survey they are trying to perform/accomplish, I have the number block permanently on my cell phone.