For devices with a SIM card slot
For devices that support mobile data services (with a SIM card slot), the SIM card from another device can also be used temporarily to reactivate the “one” app. Once reactivated, the “one” app will continue to work even without a SIM card via WLAN/Wi-Fi.
For devices without a SIM card slot
For devices that do not support mobile data services (without a SIM card slot), you can register for the “one” app for the first time via WLAN/Wi-Fi. However, it is not possible to reinstall or reactivate the “one” app on the device after, say, the app has been activated on another device in the meantime. For any new installation, a mobile phone number is required so that an SMS can be sent to the device concerned. In this case, the device must have a SIM card slot.