Re:In Belgium, they all cap. (Score 2, Informative)

The biggest (50%+ marked share) ISP in Norway, Telenor, tried something similar some years ago. There was a monthly quota, somewhat depending on your package/speed (the cheap ones had lower quota. I don't remember the exact number). If you hit the limit, the connection would drop to ISDN speeds. You could then either wait until the next month for the quota (and speed) to reset, or pay some money to add more bytes to your quota for that month. They also had a tool that measured how much you'd used, and one-click buying of more bytes. By paying some extra money each month, you could get "free" internet usage during the night that didn't count towards the download limit. It was widely despised, and Telenor's competitors took great advantage of that in their ads (Telenor was pretty much alone in limiting downloads). They were eventually forced to drop their quota system.