You don't need to be connected to the Internet all the time to use Tesla Android. You can also block FSD Telemetry and Tesla Software Updates to save your data package.
Changing network settings
1. Open the Tesla Android app in your Tesla by navigating to https://device.teslaandroid.com in the browser and tap the Settings icon in the corner.
2. Select the Settings tab on the bottom navigation bar
3. Review the Offline Mode settings. It is enabled by default to prevent the car from disconnecting from your Tesla Android device when you don't have cellular reception. Telemetry and Tesla Updates are not blocked by default.