https://fixyourandroid.com/about/oma-client-provisioning/
OMA Client Provisioning is a system-level application that serves as an interface between your phone and your wireless carrier network. It is a  standard mode of operation used by the network carrier provider to send the network configuration settings to the device while setting up the new SIM card. These settings are essential to use the SIM card for making calls, using the internet, and performing other carrier-related tasks like sending SMS and configuring the proper network etc. Every time you set a SIM card to a new phone the OMA Client Provisioning comes in the action and sends an SMS containing the configuration settings.