How to limit roaming charges for Data transfer?
Smartphones are heavily dependent on the internet and consume much more Data than the traditional mobile phones (push e-mail option, download of the whole email with attachments, free applications etc.). Please note that the roaming charges for Data transfer can by very expensive depending on the country. More details on tariffs are available here: Communication and Data transfer tariffs
The best way to avoid excessive and accidental Data usage is to disable the Data Roaming AND location services and unblock it only if needed:
Go to Settings -> General -> Cellular-> Data roaming: OFF
Then go to Settings -> Privacy -> Location Services -> OFF
You can control your Data transfer usage in the menu: Settings -> General -> Usage-> Cellular Network Data
S4 and S5: Go to Settings -> Connections -> More Networks -> Mobile Networks -> Uncheck the option ”Data Roaming”
Xcover 2: Go to Settings -> Wireless and networks -> More settings -> Mobile Networks -> Uncheck the option ”Data Roaming”
For any other device please refer to your phone user's guide.