Keep in mind that the extra GB you get with the tablet may be shareable but only 1 way. I learned this last year (unless they changed). We have a 6GB plan so I was under the impression when I talked to the reps that I was going up to 7GB shared. We went over the 6GB for the first time because our internet at home disconected and my wife didn't noticed she was streaming youtube for hours. Anyway I said to myself not to worry we have 7GB.
End up that it doesn't count toward the data used on your cell. But if you use the 1GB on your tablet and go over it jumps over your cell data.
I know it's weird. but I called to fight it and that's what I was told. I was like "what??"
anyway.. we dont use the data on our tablet anymore anyway.
Maybe I'm wrong... but that's how we understood it after we got charged.