Hello, I recall somebody at the Apple Store suggested me to buy the LTE version rather than the WiFi only version. I think he mentioned something about able to buy SIM card from Apple Store in major cities around the world and I could access the internet and pay by use. How does this work? I got the WiFi only version as I could tether it with my iPhone. Haven't opened the box yet and wonder if I should actually get the LTE + WiFi version.