Who called from 5203143076

Does anyone get an answer from this number? I answered it thinking someone from work calling me but there's no answer...

called. left no message. no caller id.

Got three (missed) calls from this number in a day--no message left.  It appears to be a landline from Tucson, AZ attributed to Level Three (L3) Communications, a company that I know to contract with the military, and potentially other government clients.  
http://www.area-codes.com/exchange/exchange.asp?npa=520&nxx=314

Upon further investigation (I called back), there was an automated message claiming to be Verizon, identifying me by name and directing me to press * (star).  I did not do it, and I don't trust it.  I have been receiving similarly suspicious text messages from "Verizon" but, when I go to my Verizon account online, there is no evidence of an alert or reason they would be contacting me.

It is Verizon's "Robo-dialer". If you call back and hist make a payment arrangement they'll take your number off the dialer. It works, I've done it