Besides all the options about the data limitations in the Policies. It would be really helpful if there was a global configurable alert that sent you an e-mail the moment your monthly data pool reaches certain % of MB used.
Even better if you could set two or three e-mail alerts, with configurable usage percentage. For instance: One e-mail alert when you reach 75% of monthly usage, another one if your reach 90%, and another one if you reach 100%.