SIM stands for Subscriber Identity Module.
SIM cards are small computer chips -- mostly coated in plastic -- that serve to connect your phone to your carrier's wireless network. SIM cards are employed exclusively in devices sold by manufacturers and service providers that utilize GSM-based technology. These phones are widely available from Motorola, Nokia, Samsung, HTC, BlackBerry, LG and Sony Ericsson. Before purchasing a new device, SIM card users must ensure the new device is a GSM phone.
GSM Explained
GSM is a specific type of wireless communications technology widely employed all over the world. Short for Global System for Mobile Communications, GSM primarily operates on 850, 900, 1800 and 1900MHZ frequency bands. With GSM devices, your wireless service is tied to the SIM card rather than the phone. As a result, your wireless service can be used with any GSM device as long as it has been unlocked for use with your carrier.
Benefits of SIM Cards
Service portability is a key component to the popularity of GSM devices. SIM cards allow users to quickly swap their service from one handset to another. In cases of device malfunction, users can simply transfer their SIM card to an alternate device until their normal phone has been repaired or replaced. SIM cards also store all of your contact information, meaning you can quickly and automatically shift your address book entries to a new device instead of manually re-entering them one by one.
SIM Card Disadvantages
The downside to this service and contact portability comes in the form of theft. Unless a SIM card lock code is enabled, it is very easy for someone to steal your SIM card and rack up extensive charges. Thieves can also gain access to all of the contact information stored on your device. This could potentially put friends and loved ones in danger if their home addresses are stored on your SIM card. Locking your SIM card is a vital precaution when it comes to utilizing a GSM device.
GSM Carriers
In the United States, two main service providers utilize GSM technology: AT&T and T-Mobile. In the past, AT&T has acquired smaller GSM carriers like Cingular and absorbed them into their network infrastructure. At the time of this writing, AT&T is also poised to absorb T-Mobile after recently purchasing the company. Both carriers offer a wide variety of handsets from several different manufacturers for use with your SIM card.
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