I can't believe this post is making the rounds again six years later. Reply All did a great podcast about a similar issue, it's worth a listen!
https://www.gimletmedia.com/reply-all/104-case-phantom-calle...
https://www.gimletmedia.com/reply-all/104-case-phantom-calle...
IIRC, the situation was brought up at a telecom conference and the calls dropped suddenly; suggesting at least one of the people involved was deep into the industry and probably at the conference. They even get an FBI agent on at one time who is convinced they'll find this person.