No idea who it is, but getting that number also. Grrrrr.

Called 5:35 PM on 2-20 and again at 12:17 on 2-24-14.  Same thing both times - answered and after a few clicks, line went dead.  no response.  Traced back - Not a valid number.  tried to call back, got message " your call can not be completed as dialed.  please check your number  and dial again"  If they are going to call, at least they could say hello.
Caller ID: unknown caller"

Exact same experience.  Call came in around 9:30 am central.  Sales call? Scam? Pollster?