Category Archives: About SIM Cards

What About SIM Cards?

A SIM card is one of the most important components of any mobile phone. Such tiny chips are essential for the majority of models to operate. How do these cards function and what are the primary purposes that they serve?

Types of Phones

For the sake of simplicity, we should mention that there are two types of mobile phone service. These are GSM (Global System for Mobile) and CDMA (Code Division Multiple Access). The GSM variety requires a SIM card to activate while a CDMA phone is automatically “locked” to a specific carrier.

The Basics

A SIM card contains information such as the identity of the subscriber as well as a validation “key” that unlocks the phone for use. While the authentication process can be quite complicated, it can generally thought of as a “request” by the card to be provided access to a certain network when the phone is turned on. If the proper credentials are supplied by the card and these are matched to those that exist within the database of the provider, the phone will be connected to the network. Essentially, a SIM card contains information in regards to a network as well as the login credentials for the user.

Flexibility and Memory

One of the advantages of a SIM card is that it can often be interchanged between phones (as the user data and the credentials are on the card itself). This cannot be performed when using the previously mentioned CDMA system. Another benefit of these cards is that they are able to store moderate amounts of data such as phone numbers and SMS messages. However, keep in mind that the maximum storage capacity of most cards is a mere 128 kilobytes of data.

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Locked SIM Cards

There may be times when a card is “locked” from use. This signifies that the carrier does not recognise the network that the SIM card is attached to. This is the main reason why some phones need to be unlocked before they can be used.

The tiny SIM card is therefore a critical component within most mobile phones. Although they can make accessing a network simple and they are able to store important information, there can be problems should the card be “locked”, lost or otherwise damaged. Without these cards, the majority of mobile communications would grind to a halt in only minutes.