If you used your brain you could store it with a series of car batteries or similar, it would allow you to have light and perhaps enough power to run a light or kettle or maybe a laptop or charge a mobile phone for a short while.

At some point you have to have a little public responsibility. If too many people tapped into this then phone prices go up to account for the increased needs of electricity - it doesn't come free from the air.

One could also do "free secret source of bricks!" and cut chunks of stone out of the highway. Or "free secret source of electricity!" by sticking your extension cords in the neighbors outside outlets.

At best it will lead to the phone company sticking meters on houses to monitor electrical use, and at worse will degrade telephone usage or dramatically increase prices.

Bad idea in my opinion.