Save on data roaming costs
Want to go easy on your phone bills? You can save on data roaming costs by changing mobile data settings. Data roaming means using your phone to receive data over networks that your network service provider doesn't own or operate. Connecting to the internet when roaming, especially when abroad, can raise data costs substantially. Your network service provider can charge you a fixed fee for data transfer or on a pay as you use basis. To use the optimal connection method, change the Wi-Fi, mobile data, and mail download settings.
Using a Wi-Fi connection is generally faster and less expensive than using a mobile data connection. If both Wi-Fi and mobile data connections are available, your phone uses the Wi-Fi connection.
On the start screen, swipe left, and tap 
Settings .
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Tap WiFi .
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Make sure WiFi networking is switched to On
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Select the connection you want to use.
Tap mobile network , and switch Data connection to off .
Tap mobile network , and switch Data roaming options to don't roam .
To save on data costs when travelling, save new maps to your phone before your journey, and browse the maps offline. If you’re running low on space, you can remove some maps from your phone.
Set your phone to check for new mail less frequently, or even by request only. In every mailbox you have, tap 
> settings > sync settings , and change the setting for Download new content .