The iPhone message “SIM Not Supported” means the phone cannot use the inserted SIM or eSIM on the current carrier setup. Learn what to check safely.
Common causes include a carrier lock, an inactive or incompatible SIM, an eSIM that was not transferred correctly, or a carrier account that needs activation.
This is different from a SIM-swap warning text. The iPhone message is a local cellular setup issue; it does not by itself mean someone has taken over your phone number.