They Call, then Hang Up so you call them back to see who it is. Once you do that you can not add them to the "Do Not Call Registry" because YOU called THEM. It's a new scam way of Calling so they can't get put on the List.
Call from this number at 7:03 p.m. on 4.7.2015. Did not answer and they didn't leave a voice mail. Not a number in my contacts and added to block list. It appears you block one number and the move to a different one. Reverse lookup on the phone number from Whitepages.com shows the call came from a landline in Kissimmee, FL