] Currently, nearly 100 per cent of broadband access is
] provided by carriers on a flat-rate basis, in spite of
] the fact that this is not the most efficient or
] economical access mode for either the carrier or the
] customer.

Of course all the right buzzwords are in this article (LDAP, QoS, rate-limiting, etc) but the fundamental issue is that public IP networks do not allow this kind of control. Simply changing some ACLs to allow you to access a video server if you pay extra is not the holy grail of metered billing.