i am wondering if its true or not , i have been taught that air is an insulator , if a such device exists then we could transport electricity without wires? and the people in its path of flowing will get electric shock?
There are methods out there for collecting free electrons from the air (static buildup) you can also generate electricity from the radio waves in the air. I once built an AM Radio receiver that required no batteries as a child.
There's problems though, the amount of electricity generated is extremely minimal from either of these methods, and the former is highly susceptible to current weather conditions. The example of a crystalized AM Radio goes back to the 50's even, but produces an audio signal that's barely audible through a small monophonic headphone.
So yes you can get electricity from the air, but to get enough to power anything more than a wrist watch would require so much wire strung through the air as to make it completely impractical. Getting enough electricity to power your house this way would require thousands of tons of copper wire, more than most could probably fit on a small quarter or half acre lot.
As for transmitting all electricity for homes through the air from generator stations that wouldn't work either. This is because the path that electricity naturally wants to take is back into the ground. Electricity also takes the the path of least resistance which is why in the home the power travels back out your house through wires, it's easier than going through the air to the ground. However, produce enough electricity without any place for it to go, and you'll get what is essentially a lightning bolt from the generator to the ground.
I think what your friend owns is a plug in battery pack for his phone...you can buy portable devices that can add a little power to your mobile but they themselves are battery powered and so do not last very long...i seriously doubt he has something that can draw electricity through the air to his mobile because, as you said, anybody in its path would be electrocuted...either that or he's lying...that's always a possibility...