The location of call origin is normally determined by the outgoing caller ID of the caller but can also be determined by GPS position or signal triangulation, the latter being particularly useful for calls coming from mobile phones.
For instance, a different caller route can be defined for each country that a call could originate from.
This would be done using the international dialling codes of the incoming caller ID.
The furthest that can be gone is to program in separate destinations for individual telephone numbers that call in.
Systems can also be programmed to send callers that withhold their caller ID down a specific route, thereby acting as an anonymous call rejection device.