Running applications directly on the IoT device - close to the modem and sensors at the network edge - brings benefits like improved link budget and longer battery life. The application environment on which the application code is executed determines to which extent these benefits can be materialized. In this talk we briefly walk through the various application environments ranging from scripting engines on the modem to dedicated host microcontrollers with native SDK. These variants trade off cost, software flexibility, and energy efficiency. We highlight which variants are best suited for which use-case and point out the u-blox way on Edge computing in cellular IoT.