What is a "Subscriber Identity Module" (SIM) card?

What is a "Subscriber Identity Module" (SIM) card?

TJ McClearin (Business Manager, Infinity Wireless, LLC) gives expert video advice on: How do cellular phones work?; What is the difference between a "locked" and an "unlocked" cell phone? and more...

With cell phones, SIM actually stands for Subscriber Identity Module. Essentially, a SIM is like an ID card for your telephone number, and that ID card is specific for the network. When you sign up with a new service on a GSM carrier, GSM carriers use SIM cards to define who people are. So, when you give me your name and I set up your account, the SIM card number that I put in there is your unique identification for the network. Once your cell phone's turned on, it actually takes that unique identification and sends it to the network so that the network knows who you are and where to route the phone calls to.