So you wanted S4->wireless->iPad Mini? Yeah, pretty sure you're going to need to root it for that. Unless you can find an app to make it transmit wireless. The only way I can think that you could get this to work would be to tether a computer from it (either USB or Bluetooth, doesn't matter), then have the computer somehow transmit ("transmit" == act as wireless server, since it's really both transmit and receive, but it still has to be the master and server-provide stuff like DHCP) via wireless.
I ended up giving up my limitless plan -- I had them do a history, and I never even came close to their smallest limit. You may want to have them do the same thing. I could only go back a couple months online, but they can get a report and email it to you if AT&T are the same way.