Fair Usage Policy (FUP) reduces headline speed after you reach 70% of your monthly data limit and then suspends service when you reach this limit. You can purchase GByte Boosters to continue with services.
Volume Based Billing (VBB) does not change your headline speed and service is never suspended. You will be charged for any excess GByte data usage the following month automatically.
You always have access to the portal page to see how much you have used even when you have been suspended under FUP.