https://www.techradar.com/news/vodafone-and-deutsche-telekom-test-nb-iot-roaming

Vodafone and Deutsche Telekom have completed the first international roaming trial of Narrowband IoT (NB-IoT) technology in a development that could accelerate the development of cross-border IoT services.

Roaming is seen as an essential component for licensed mobile IoT networks, with applications such as logistics tracking needing to work in multiple territories. It’s also essential if equipment manufacturers are going to achieve economies of scale with devices like smart metres.