Nice. We had this in the 90s in Holland. It was called chipknip. (Knip is old slang for wallet).

It was really like digital cash, the money was loaded onto a chip. So if you lost it you lost all the money. There was no pin code either, just like a real wallet. Unfortunately it was not really anonymous because the Dutch government are really into surveillance.

It didn't really last very long, it was only popular for parking machines. In those days 2G was expensive so validating transactions online was rare.