Building realtime mobile apps presents several challenges. Most approaches default to complex polling and caching techniques, and/or use subpar toolchains. This talk argues that functional programming is the best way to build scalable mobile apps. The talk demonstrates how to quickly build a realtime cross-platform mobile app with React Native. In addition, it describes how to use Elixir and the Phoenix framework to drastically reduce the effort and complexity necessary to build a realtime web server. Lastly, the talk argues that this approach is the most maintainable for small to medium-sized development teams.