SIM cards are always used on GSM phones; for CDMA phones, they are only needed for newer LTE-capable handsets.
SIM cards can also be used in satellite phones, computers, or cameras.
Follow these steps if you get an error message in SAM.
The first UICC smart cards were the size of credit and bank cards; sizes were reduced several times over the years, usually keeping electrical contacts the same, so that a larger card could be cut down to a smaller size.
A SIM card contains its unique serial number (ICCID), international mobile subscriber identity (IMSI) number, security authentication and ciphering information, temporary information related to the local network, a list of the services the user has access to, and two passwords: a personal identification number (PIN) for ordinary use, and a personal unblocking code (PUC) for PIN unlocking.
This means you can just take out your ATT sim card and use a T-Mobile SIM on your i Phone, for example.
Unlocking an i Phone is great for those who want to use a different carrier than the one their i Phone is “locked” into at the moment.