I can't see any big deal. I have left my phone on by mistake before, nothing happened. The worst case scenario is either you'll have a flat battery, or you'll end up with a massive bill when flying to less enlightened parts of the world.
We have a LIDO/Panasonic Toughpad EFB solution at my airline and the plan was to connect these two devices either side of the cockpit by Bluetooth so the PNF can ping the ground charts (etc.) to the PF when appropriate. This hadn't been taken up due to the standard legislative delays but as I understand, it is a feature that has been designed into the LIDO system.