I believe Copenhagen has this too now. I visited in the same week they were launching the system (last year?) and it worked perfectly. All you had to do was pre

I believe Copenhagen has this too now. I visited in the same week they were launching the system (last year?) and it worked perfectly. All you had to do was press a button on your phone as you enter and leave the station and it automatically calculates what you owe. I loved it. It also worked throughout all of the different train systems.