If you’re an active mobile phone user, you will notice that your phone can actually make emergency calls without any SIM. I know you must be wondering how this is possible since there’s no mobile number. Let me explain how your SIM works. SIM as you ought to know stands for Subscriber Identification Module and it helps to identify the cell service subscriber that is trying to connect to the network. Every user has their own SIM, so network providers can direct calls to that specific phone and track usage (and charges) individually. The identifying number of a SIM card is called an ICCID.