In recent years phones have started getting an eSIM chip built-in to the phone which is a modern replacement for a physical SIM card you slot into the device.
Unfortunately until recently managing these eSIMs (installing a SIM card from your operator, enabling or disabling the card) was limited to proprietary apps shipped with Android.
Let's talk about how eSIMs work on a Qualcomm phone using 100% open-source user space and mainline Linux kernel, and what QMI and QRTR are doing in this stack.