Google Now or S Voice

[stooler]

With my new S4, I have read that I can use either of those two functions to voice command my phone (that is Bluetooth paired in my truck) to dial contacts. Will both of these (Google Now or S Voice) work on major highways all over the USA, or do either of them require WiFi?

 

[UJ95x]

Welcome to AC
They will both work as long as you have service. I (and I think most here would agree) find that Google Now is far better than S Voice.