I noticed my new Verizon iPad came with Data Roaming defaulting to off. What does this mean? If I'm somewhere in the US that doesn't have Verizon coverage but does have roaming coverage, is that data usage included in my Verizon plan? If so, why would I want to turn roaming off? And outside the US, I assume any data there wouldn't work on my plan anyway, so it shouldn't matter whether roaming is on or off. What am I missing?