blackjack17:
Which limits what they can do on the net. Being able to roll over my allowance would be a huge advantage. Some months I use less than 20 other months more than 200 (meant to be 120 but due to the vodafone cut off bug I get around 200 (what i assume is a bug)).
Usage like this is exactly what ISP's don't want, and if plans and users were like this you'd be paying a lot more for your service. There is no way you could forecast upstream bandwidth if this occured.