They didn't leave a message.  Called it back.  It was the pre-recorded operator message with the little tone that sounds like ascending pitches of three, 'doo, Doo, DOO' at the beginning, followed by the ever famous,
    "We're sorry.  Your number cannot be comlpleted as dialed.  Please check the number, and dial again."  Then, "message CI20,"  or some combo of numbers and letters, I don't remember exactly what they were, but for the accuracy of leaving this note about it here, I called back again (just a few minutes later), to find out, and recieved the fast busy signal dial tone.

who called me and why

none