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.