One of the most dangerous things you can do in a thunderstorm is to use electrical equipment that works from the mains. That is equalled by using telecommunications equipment that involves wires, even if they're buried under the ground. If the lightning stirkes the cables (and the ground isn't even there, for the lightning), you can get many millions of volts up your armpits.
It is on a par with flying a kite with a wet rope into a thunderstorm.
The trouble is that the cables offer one of the best paths for lightning and will get struck out of all proportion, in preference to other objects. If caught in a thunderstorm and there are cables underground and trees nearby, well, you're going to go out with a bang, probably.
If the hairs on your head start to rise, immediately drop flat on the ground. You might just be lucky...