Transit operator (carrier) – a company that earns on providing mobile operators favorable (cheaper) route for a call from one country to another. It doesn’t have its own subscribers, towers and SIM’s.
The role of the transit operator in the telecommunication market can be compared with the tour operator, where the role of tour operator implies a transit operator, whereas a call means is a client. As we know, the tour operator does not have its own hotels, airplanes and taxis. Its task is to make secure and inexpensive route for the customer traveling on vacation.
In this scheme you can see how carrier earns money.