You write "The device has 2 SIM slots and one SD (memory expansion) card slot, so the phone can hold 3 cards at the same time. This is not quite true: only one physical SIM card and one physical SD card are possible. The manufacturer's website mentions the possibility of an "eSIM" card: https://support.fairphone.com/hc/en-us/articles/4405550572177-FP4-Set-up-eSIM-card-embedded-SIM-