This document discusses sim box fraud, which involves using sim boxes and sim cards in gateways to bypass international carriers and terminate low-cost traffic. Sim box operators are able to make a profit by exploiting the difference between high mobile termination rates and lower retail call rates. This fraud causes revenue losses for mobile operators who miss out on termination fees, and can amount to hundreds of thousands of euros per month. The document outlines the infrastructure used by sim box operators, how they route traffic, and some methods for detecting and addressing sim box fraud.