What Is a SIM Card for a Cell Phone?by Jessica Cook
If you purchase a cellular phone with a calling plan from a major service provider, chances are your phone will come with a SIM card. This card holds data for your phone and identifies your phone number, allowing it to work properly. A SIM card also keeps your phone linked to your service provider.
"SIM" stands for Subscriber Identity Module. Essentially, it provides the identity for your cell phone.
Your SIM card stores and identifies your phone's number. If you switch to a different cell phone model within the same service provider, you can install your old SIM card into the new phone and your number will remain the same.
A SIM card can store up to 250 contacts, so if you store your address book information on your SIM card, you can transfer all of your contacts from phone to phone as well.
Your SIM card links your phone to your own service provider, and activates your phone for use with that provider. A SIM card for one provider will not work in a phone that was purchased from another provider.
If you have an unlocked phone (not associated with any particular service provider), you can purchase prepaid SIM cards when you travel and your phone will always have a local number to the area you're in.
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