I have just bought Orange (UK) Micro SIM for my iPad, because 5p/ per MB cheap and pay as I use iPad plan.
I have noticed that maybe iPad use Cellular data before Wi-Fi start??
My iPad is in my house and always use Wi-Fi at home connected, still if I check the usage/ cellular Network Data/ received...I am using about 1Mb a day. I checked usage with Orange. Yes I am paying. It is connected to Orange but connected to Wi-Fi too. I thought use wifi all the time if connected.
But seems like check Cellular data first?
Maybe push Notifications or something use Cellular data before Wi-Fi start?? or when iPad is sleeping?
It's not expensive but I may try Cellular data OFF at home all the time.
I know that I can make Cellular data OFF.
And only WiFi maybe at home and when I am out side make Cellular data ON.