There are different ways of doing it, depending on the model of S4 (IOW, who your carrier is).
But if your carrier blocks tethering without a tethering account, it's definitely going to block a Nintendo - that looks (to the gateway) nothing at all like a cellphone. You can fake it with some web browsers on a laptop or desktop, you will probably get away with some things that run on a phone, like email, Akype, etc., but not a game box.
But until FoxFi updates to 4.4, how you do it still depends on who your carrier is.