You can cut data roaming costs and save on your phone bills by changing mobile data settings. To use the optimal connection method, change the Wi-Fi and mobile networks 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 increase data costs substantially.
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.
Connect to a Wi-Fi network
Tap Settings > Network & Internet > Wi-Fi.
Make sure Wi-Fi networking is switched to On.
Select the connection you want to use.
Close the mobile data connection
Swipe down from the top of the screen, tap network_cellMobile data and switch Mobile data off.
Tip: To follow your data usage, tap Settings > Network & Internet > Data usage.
Stop data roaming
Tap Settings > Network & Internet > Mobile network, and switch Roaming off.