@neil Do you know if the successful calls are over a 2G/3G signal, or using VoLTE (4G calling)? I understand the UK is in the process of shutting down 2G/3G networks, but not sure about that particular carrier at the moment. The issue in the USA is that 2G and 3G have been shut down, so VoLTE functionality is needed here. But I know things vary by country and even carrier.