The use of a Trusted Execution Environment (TEE) of a user device to perform Universal Integrated Circuit Card (UICC) update may replace the conventional use of multiple SMS messages to update the UICC of a user device. A UICC update request may be sent to a UICC update service of a wireless communication network via a communication session by a trusted update application that is executing in the TEE. Subsequently, the UICC update service may send a UICC update file to the user device via the communication session for storage in the TEE. A copy of the UICC update file is then transferred from the TEE to modem software of a modem in the user device. The modem software chunks the UICC update files into multiple UICC update data chunks. The data chunks are sent by the modem software to the UICC to update the UICC.