This document specifies a low-level API for the minimum UICC functionality needed in low-cost constrained IoT devices. This includes functions for network attachment and functions for cellular subscription profile download and management. To reduce the cost of a constrained IoT device, the UICC functionality is likely to be an integrated part of the application processor or the modem of the IoT device. The realization of the UICC functionality may vary with the device vendor or modem vendor. The API hides the realization and location of the UICC functionality from its users, even when a dedicated component is used to realize the UICC functionality.