Called, did not leave message. Turned out it was a technical recruiter from Oxford. Probably need to lecture them about leaving voicemail or sending email, but at least it wasn't a crank call. I decided to write it up because I saw some reports on other sites that were inconclusive. 800notes appears to be the most useful and complete site for this sort of thing.
Call type: Contract opportunity (I passed; I'm not available for contract work at this time). That does not appear to be an option in the drop-down box below.