I didn't actually answer it, and no voice mail was left. Had odd feeling about it, so I Googled the number.
Obviously this guy has some sort of issue with Energy Workers and the like. I would advise those who are being called by this person, turn around and call his local police department, as well as your own. It's a Virginia Number, but it traces to San Jose, CA http://www.namethatnumber.net/phone-call/1-408-439-9131. You can also call CINGULAR WIRELESS who appears to be his carrier. If he's making death threats like some have claimed on various sites, I'd also advise to taping the call so you have that for the police.
Here's some information on how death threats are viewed by law in California where this man seems to be located:
http://www.danieljensenlaw.com/articles/death-threats/
Also Here's one on Stalking and Harassment Law in California which his behavior also falls under:
http://www.internetlawyer-blog.com/2011/12/ca ... sment-laws.html