Same as everyone else on this list: let phone ring, since I didn't recognize the phone #; they didn't leave a message. The only interesting part of the call is that it went to my cell phone, which I never use and never give the number out.
Called me, didn't recognize the number, so I rejected it. No voicemail. After reading these posts, I promptly blocked the number. The fact that they called me on a sunday evening is also a dead giveaway...