To turn off data
roaming follow this instruction path:
Settings > under Wireless and network select More...
(A prerequisite to proceed
is that Flight mode is deselected. (Flight/Airplane
mode toggles all communication.)
> Mobile Networks > then
deselect "Data roaming"
Data roaming should always be left
deselected, unless your device has been unlocked from your cell provider, or
you are rich enough to buy a suitable roaming plan from your existing cell
provider.
Now that you're data roaming safe, read on for how to further control
mobile data usage.
Anytime you don't want mobile data (roaming or not) at the same path as
above deselect "Use packet data".
There is the possibility that yourself or a process could toggle packet data
on it's own agenda. So to avoid a data leak while roaming. you should have
deselected "Data roaming" before turning
off "Mobile data".
The "Use packet data" is also user toggled by "Mobile data"
on the pop up notifications menu.