Some wireless(cellular) ISP's in the States will slow down your connection when you hit the limit(no overage charges on some). Instead of just letting the user run full speed and really racking up the overage charges.
Telus gives users a free first month of technnically unlimited GB's to let the user understand how much data they can do via the wireless stick. And now a floating pay limit to the next GB pay scale(500MB, 1GB, 2GB, 5GB), if the user goes over their bottom plan of 500MB's.
There is a slow worldwide movement to actually warn users that they are about to hit their limit. And possibly shut it down when roaming in another country. To prevent massive charges of $10,000 for data use.