Telephone companies in different countries use a variety of international telecoms routes to send traffic to each other.
For example, BT and the Australian carrier Telstra send each other traffic over a satellite link or by submarine communications cable.
Minutes exchanges allow carriers to buy and sell termination anonymously at a contracted price and quality.
The anonymity is important, as minutes exchanges are used daily by PTT's and Tier One carriers to manage their commitment deals.
Re-origination is made possible by exploiting the functionality of the SS7 signaling system, which allows a great deal of call information to be transmitted.
This is of course not allowed by the local regulator and also the receiving carriers prefers the higher international rates, but since the black action is done in a switch owned by a person or company who is willing to break the law, this is usually outside of the view of these parties and thus enforcement can be difficult.
Grey routes can be prevented by good Fraud Management or by regulators or carriers opting to close the gap between the international and domestic tariffs.
With a small satellite dish on the roofs of its offices in country A and B and a little capacity on a transponder, a company can become a small-scale international carrier.
There grey market setups are popularly known as illegal International Long Distance (ILD) telephone exchange.
[1][2] Voice calls can be compressed and packaged into voice-over-IP packets and sent over the public Internet or a more direct IP-based data link, thus by-passing the conventional telephone routes into a country.