When traveling outside the European Union, using a travel eSIM can help avoid expensive out-of-plan charges. While mobile providers are required to stop data usage once the monthly limit of 50 euros HT (60 euros TTC) is reached, some travelers have faced unexpected bills in the thousands upon returning from their trips. This limit can be raised if the customer agrees, but it’s better to avoid such situations altogether. A good alternative is to use a special travel mobile plan found on price comparison websites. However, simply installing a travel eSIM isn’t enough to prevent out-of-plan charges. The smartphone must be configured so that the main SIM or eSIM doesn’t use data in the background—for example, for app updates, cloud synchronization, or receiving MMS and emails. There are several ways to manage this without staying in airplane mode the entire trip. A travel eSIM can be installed before departure and only connects to a network once the traveler arrives at their destination. However, users should be careful with global or regional plans that include France, such as an eSIM Europe. These should not be activated before the trip begins, as their validity period would start too early. Before departure, it is important to know the essential settings for both iOS and Android devices to avoid unexpected charges. On Android smartphones, there are two main ways to configure a travel eSIM properly. The first method is to completely disable the main SIM or eSIM. This can be done by going to Settings, then Connections (or Network & Internet on Google Pixel devices). On Samsung Galaxy devices, users should go to SIM Manager and uncheck their main line to make it completely inactive. On Google Pixel devices, users should open SIM Cards, select the operator of the main line, and disable the Use SIM option. The second method is to disable only the mobile data of the main SIM or eSIM, allowing it to continue receiving SMS messages, which might be necessary for authentication or bank alerts. In the SIM Manager menu, users should first ensure the travel eSIM is selected for mobile data and then uncheck Data Switching. This prevents the phone from using the main line if the eSIM loses network coverage. It is better to avoid using the Roaming Data option, as it may not target only the main line and could affect the eSIM’s connectivity. On Google Pixel devices, the Roaming option can be set line by line, allowing users to turn it off on the main line only. On an iPhone, the process is similar. Users should go to Settings, then Cellular Data. From there, they can either completely disable the main line or just disable mobile data to continue receiving SMS. To disable the main line, users should select it in the SIM Cards section of the Cellular Data menu and uncheck Activate This Number. This makes the main SIM or eSIM completely inactive. Alternatively, users can uncheck Data Roaming in the Line Options menu to prevent the iPhone from using mobile data when it detects a foreign network. To disable only the mobile data of the main SIM or eSIM, users should select Cellular Data in the Cellular Data menu, ensure the travel eSIM is selected, and uncheck Cellular Data Switching. This prevents the iPhone from connecting via the main line if the eSIM loses network coverage. While keeping the main line active allows SMS reception, it also carries risks. The 50 euros HT (60 euros TTC) limit applies only to data, not to calls. Calls made or received outside the European Union are charged out-of-plan without an automatic cutoff. It is better to let the phone ring and use a messaging app instead, which can use the eSIM connection. Finally, activating airplane mode before takeoff is recommended, as smartphones can connect to satellite networks on planes and boats, leading to expensive satellite-based charges for calls, SMS, and data.