What Are Sim Cards?

By Author: Neo Nashville
Total Articles: 30
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The first SIM card was invented in 1991 by Giesecke and Devrient smart card makers. Its initials mean Subscriber Identity Module, and as the name suggests, the cards are used to store phone subscriber identification details.

These details include a unique International Mobile Subscriber Identity, or IMSI, number. The first three digits of which represent the Mobile Country Code, the following two represent the Mobile Network Code, and the last ten digits represent the mobile station identification number.

As the unique details of each phone user are stored on their SIM card and not their mobile, this means that a user can simply remove their SIM and transfer it to any other phone if they want to use it.

Each contact is stored as a simple name and number pair so that phone users can access the phone numbers of friends and relatives by simply scrolling through their phones rather than having to carry numbers around separately in an address book or diary. The number of contacts and messages that can be stored varies from phone to phone but nowadays most SIMs can store over 250 contacts and messages.

You ...
... may have heard people talking about their phones being locked. This is most usually in the case of pay-monthly phones. Locking a phone to a SIM means that that particular phone will only work with that particular SIM meaning that the customer cannot switch phones or networks.

The phones given out by mobile network providers to their pay-monthly customers are usually free, or of a subsidised cost, and so they use SIM-locking as a means of payment security. This way the network can be sure of recouping the cost incurred in offering the phone for free.

Nowadays it is easy to walk into almost any mobile phone store and purchase a single SIM card without a phone, in almost any country. This means that travellers, who have first paid to have their mobile phone unlocked to accept any SIM, can use these local SIMs in their own phones.

These SIM-only offers allow travellers to benefit from far lower international call costs, and keep in touch much more economically while on holiday.
Vodafone stock a great range of phones if you are looking to upgrade, or sim cards if you already have your phone of choice.