In the world of mobile phones, there are two primary phone types that
are available to consumers: GSM (Global System for Mobile Communication)
and CDMA (Code Division Multiple Access). GSM phones are the ones that utilize SIM cards while CDMA phones do not.
SIM cards are the small cards which contains a chip that must be inserted into GSM phones before they will work. Without a SIM card, a GSM phone won’t be able to tap into any mobile network. The card is what holds all of the critical information.
For comparison sake, CDMA carriers keep a list of all phones that are allowed to use their network. Phones are tracked by their ESN (electronic serial number) so they do not require SIM cards. Once activated, a CDMA phone is tied directly to that particular carrier’s network.
The important part is a small integrated chip which is able to be read by the mobile device it is inserted into, and contains a unique identification number, the phone number and other data specific to the user it is registered to.
The SIM also contains a small amount of memory which can store up to 250 contacts, some SMS messages and other information used by the carrier who supplied the card. A SIM card can usually be removed from one handset and inserted into any other compatible handset, allowing the user to switch devices without losing their contacts data, having to change their phone number or start a new mobile contract. This isn't generally possible if the cell phones originated in different countries, as cellular network frequencies vary between countries.
In many countries, SIM cards and handsets are locked to the carrier they are purchased from. This means that although a SIM card from a carrier will work in any handset sold by that same carrier, it will not work in a handset sold by a different carrier. It is usually possible to unlock a cell phone with help from the carrier.
SIM Card Sizes:
The SIM card size that most people use is called the Mini SIM, but Micro SIM cards are increasingly being used in mobile devices, including some models of the iPhone and the Samsung Galaxy S3. The first SIM cards were roughly the size of a credit card, and many Mini SIM's are still supplied with this large, Full SIM surround. Both Mini and Micro SIM cards feature a cut off corner to help prevent incorrect insertion into the phone or tablet. You can see the dimensions of the different types of SIM card below.
Full SIM - 85mm x 53mm
Mini SIM - 25mm x 15mm
Micro SIM - 15mm x 12mm
Nano SIM - 12.3mm x 8.8mm
Despite differences in size, all SIM cards contain the same types of identifying numbers and information on the small chip. Different cards do contain different amounts of memory space, but this has nothing to do with the physical size of the card. A mini SIM can actually be trimmed down using scissors to turn it into a micro SIM, as long as it is only the plastic surround which is cut.
SIM cards are the small cards which contains a chip that must be inserted into GSM phones before they will work. Without a SIM card, a GSM phone won’t be able to tap into any mobile network. The card is what holds all of the critical information.
For comparison sake, CDMA carriers keep a list of all phones that are allowed to use their network. Phones are tracked by their ESN (electronic serial number) so they do not require SIM cards. Once activated, a CDMA phone is tied directly to that particular carrier’s network.
The important part is a small integrated chip which is able to be read by the mobile device it is inserted into, and contains a unique identification number, the phone number and other data specific to the user it is registered to.
The SIM also contains a small amount of memory which can store up to 250 contacts, some SMS messages and other information used by the carrier who supplied the card. A SIM card can usually be removed from one handset and inserted into any other compatible handset, allowing the user to switch devices without losing their contacts data, having to change their phone number or start a new mobile contract. This isn't generally possible if the cell phones originated in different countries, as cellular network frequencies vary between countries.
In many countries, SIM cards and handsets are locked to the carrier they are purchased from. This means that although a SIM card from a carrier will work in any handset sold by that same carrier, it will not work in a handset sold by a different carrier. It is usually possible to unlock a cell phone with help from the carrier.
SIM Card Sizes:
The SIM card size that most people use is called the Mini SIM, but Micro SIM cards are increasingly being used in mobile devices, including some models of the iPhone and the Samsung Galaxy S3. The first SIM cards were roughly the size of a credit card, and many Mini SIM's are still supplied with this large, Full SIM surround. Both Mini and Micro SIM cards feature a cut off corner to help prevent incorrect insertion into the phone or tablet. You can see the dimensions of the different types of SIM card below.
Full SIM - 85mm x 53mm
Mini SIM - 25mm x 15mm
Micro SIM - 15mm x 12mm
Nano SIM - 12.3mm x 8.8mm
Despite differences in size, all SIM cards contain the same types of identifying numbers and information on the small chip. Different cards do contain different amounts of memory space, but this has nothing to do with the physical size of the card. A mini SIM can actually be trimmed down using scissors to turn it into a micro SIM, as long as it is only the plastic surround which is cut.
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