Today, I’ve found this articles from my old documentation. I hope it useful. Contrary to popular belief, BT phone cards do not work using a magnetic strip system. The reason for this being that a magnetic strip would be  read only. So how do they work then? Well, examine a phone card - preferably a used one if you are going to scratch it or dissect it. If you look on the printed surface (the green  side - which is the front) you will find two lines which form a thick band...