Are you really too lazy to research it yourself? 5 minutes of Googling brought me the answer. I mean really.
I hope you realize that Amazon will know exactly what you are doing, and know that it is you. When you register the device under your name, it gives them a way of identifying who is using what. Probably at minimum they will deregister your device and put a hold on your account.
Also, it is just a ****** thing to do. They are providing it to you for free, and you still want to exploit it. iPhone tethering and that sort of thing may be a grey area, but in this case, it's black and white.