This document discusses the challenges of interoperability between mobile devices and SIM cards. It provides statistics on the most popular mobile devices by country. It notes that standards in the industry often leave room for interpretation and competing standards. The document advocates for a "device capability server" that could detect device changes, configure devices and SIMs remotely, and help overcome interoperability issues between devices and SIMs from different vendors. It also introduces Sicap, a company that provides device and SIM management servers to mobile operators.