In a power cut, the phone system keeps on working. But most modern phones need a power supply, so I keep an old phone just to use in a power cut. I have a car battery and a DC/DC converter that provides a DC out at any required voltage (19V for my laptop or 12V for the BTB Smart Hub).
Will this work? In some power cuts, we also lose the cell signal. I know I can use my mobile phone with tethering but not always.