You can use as much data as you want. 1GB is added to your balance at the start of the month. Every time your balance falls below 100MB we add another 1GB to your line automatically.
Once you've used 8GB of data in a month, your data charge is capped at $64 for the rest of the month, but you continue to get full-speed data service. Slow down after 30GB.
If your Bill Protection is disabled, Unlimited mode will not turn on and you will use as much data as you need.