There are few alternatives to block such calls. May this options in the link below will help you.
http://vontech.blogspot.com/2012/12/vonage-specific-call-block-feature.html
Plus I use Magic Jack for phone and my caller ID only says INCOMING CALL unless I am at computer screen and I wasn't but it really only shows the number calling unless I have added to my contact list, hence the "assume Vonage" as u all say above.....hope they go away!
just called back on this number first got a spanish speaking message then they ask you to input your vonage number if not a customer put in your number you are calling from to switch over to vonage. It is a scam to get people to sign up .so ignore this number or get caught up in their little ploy to get you signed up for their service.