Instant messaging is dominated by a few large platforms, including WhatsApp and Messenger, where strong network effects make it difficult for new apps to compete and grow. The EU’s Digital Markets Act (DMA) is beginning to change this by requiring major platforms to interoperate with smaller ones. This creates new opportunities for innovation, allowing users of new apps to reach their existing contacts without having to convince them to switch. At the same time, interoperability raises important questions. When messages flow across platforms, people may face new risks and misunderstandings around privacy, personal expression, and social boundaries. In this talk, I explore these questions and share early insights from the DFF-funded mInt (Messaging Interoperability) research project, focusing on how interoperability can be designed to better support users, reduce the power of network effects, and enable people to choose messaging apps more freely.