What is a SIM card used for? A SIM card, or a subscriber identity module/subscriber identification module, is a tiny memory card that contains unique information and is linked to a particular network ...

We previously reported that a tiny handful of iPhones shipped without SIM cards, while significantly more units have generated the error message "No SIM card ...

When you use an iPhone for the first time – whether it's a new iPhone fresh out of the box or a used phone that you've gotten from another user – you need to activate it to set up cellular service.