[graf_von_anonym]

The hardware used for STM should be able to tell Virgin when you've been traffic managed and for what. That's almost certainly linked to your modem's MAC address, which should be associated with your account. What probably presents the technical challenge is pulling that data off the UBR/CMTS in real time, feeding that through the account, and then putting it into somewhere accessible to the customer. I've no idea how complex Virgin's billing system actually is, but I suspect such a process would involve yet more tiers added to what I imagine is a legacy system riddled with cruft.