There is no need to set up the CF rule again every time. This consumes time and battery a lot. We get the CF status with `getCallForwardingOption()` function from the network and we set CF status with  `setCallForwardingOption()` to the network as well. This involves radio operations, time and battery. That's a wrong idea for showing the CF. AFAIK you can use asyncStorage in Settings App, just add it in index.html as other part of the Settings apps do.