Basically here's the quick version....

Normal inbound outbound calls always hit "core routing" servers beore going to the sip proxy ones that you guys register on. All accounting/call log stuff is done on the core servers right now.

Internal VOIPo-VOIPo calls don't hit the core servers since they stay on the SIP proxy when it detects it's local.

When we roll out the new billing system, accounting/CDRs are handled a little differently and this will be fixed then.