They do not use GPS for timing, due to need for antennas. The raw data is available for public access. It is basically BGP data. There are Gbytes of it. In NZ they have to pay for their own use, so they had to get accounting going early on.
Billing is one of the things one gets out of accounting.
Network accounting relies on measuring traffic flows. Flows relate naturally to user tasks. Can select flow by application. Architecture consists of meters, meter readers, and managers. Use third quartile day measures to get round burstiness and encourage spreading the load.