BlakJak:This is not quite correct. Once you have registered (roaming network VLR, home network HLR), there is no signalling happening for a local call. Billing is delayed off-line.
If the calls didn't touch NZ systems, Voda NZ would have fun trying to charge for the call. :-)
Inversely, someone calling your NZ Mobile number will find their call routed to the switch equipment in NZ, which then has to realise you're infact roaming and redirect the call to the network currently hosting your phone. So being able to 'talk home' is pretty important.
VFNZ would not see a signal about a local call in progress.
For inbound roaming, you are correct, although some operators in some countries allow for non-tromboning roaming calls by dialing a prefix which will trigger a lookup in the VLR for the subscriber.
[nb. This assumes an SS7 based network, not an IMS/IP based network. You could, as someone else mentioned, transport your SS7 signalling over SIGTRAN as well. I wonder if the problem has been that VFAU/VFNZ did not turn up sufficient TDM links for signalling traffic, although I'm curious how roaming relationships and signalling is actually managed. Is there something like the old "GPRS Internet Exchange" for it?]


