SBB FreeSurf APP
Passengers from abroad will be able to surf the internet for free with a SIM card (also eSIM) from a mobile phone provider participating in SBB FreeSurf. Trains with a free internet connection are marked with «FS» (for FreeSurf) in the online timetable.
When boarding the train, the customers can open the SBB FreeSurf app. Automatic recognition takes place using a beacon. After registering successfully, the customers will receive an SMS text confirming that they can surf for free via their mobile phone provider. When alighting from the train or switching off the connection, you will receive a message stating that free internet access is no longer active. We only need customers to provide the mobile number to be used for registration.
https://www.sbb.ch/en/station-services/during-your-journey/on-board-service/freesurf.html