Can we trace the orginating country of a VoIP call?

Hi Everyone, I work in a Telco as part of their assurance team. I was wondering if it possible to trace the call back to its originating country.

We provide solution as a product to small time resellers that don't have an operator level infrastucutre. Those resellers can host their numbers on our network and we take care of the termination of the call to its destination.

Since the numbers are hosted on our switch, that switch poses as the originating POI (point of interconnect). I am aware that NetOps use signaling tools to trace the call but in this case the customer (reseller) is hosted on our network.

As part of assurance, I always wonder what if the resellers are sending us manupullated traffic. Those who are fimilier with telecom voice business must be aware of origin based billing where not only the terminating destination but the origin as well considered to charge for that call.

For example, a call originated from Uganda for UK, and this reseller (customer) of ours managed to get the call to France at his exchange over public internet, and from there forward he has taken the service from us, and its our job to terminate the call to UK. Resller is aware that Uganda is a country which has surcharge rating (origin based billing) cause we have mentioned that in the tariff, so what if he manuplates the number and changes it to a french number or some other non-surcharge origin number in such a way that it does not look invalid but is not the orginating number either (such as grey traffic using sim boxes).

Is there any possible way to capture such type of fraud? By the way, since its VoIP traffic we use IMS switches such as SONUS GSX.