What is a SIM card?

Answer

A SIM card is short for Subscriber Identity Module card. It is a tiny encoded circuit board which is fitted into GSM cell phones at the time of signing on as a subscriber. It holds the details of the subscriber, security data, and memory to store personal numbers. A SIM card stores information which helps the network service provider to recognize the caller. Whether it is a plug-in type or credit card sized, it retains the same uses.

A SIM card is a removable memory card and can be put into any compatible GSM handset, permitting the user to keep the same number while changing handsets. It is a standard unique chip which is a must in every GSM cell phone.

The working of a SIM card

A SIM card is a digital identification chip in cell phones. The validation and encoding ability of a SIM help to stop your cell phone from being stolen and your conversations from being overheard. The SIM stores personal data, user ID and billing information and can be interchanged between phones. So you can easily receive personal calls even while using someone else's phone just by installing your unique SIM in that cell phone.

Some cellular phone carriers sell phones in a "locked" condition (either locked in with a particular service provider or a specific SIM). If you have such a cellular phone then you will not be able to use different SIM cards with it unless you can "unlock" your phone.

If you have a country specific SIM card then it will most likely work only in the country of its origin. A U.S. specific SIM card may give you limited coverage while traveling through Europe or some of the Greek Isles. Most country specific SIM cards have voice mail so a caller can leave you a message if your cell phone is turned off or not reachable.

SIMKey Keyring Databank

Ever misplaced your cell phone or had it stolen? Well, buying a new cell phone is bad enough but trying to replace all the numbers stored in your old SIM card can be an impossible task. A SIMKey Keyring Databank is a novel device which helps you to backup your SIM data so that you never have to worry about losing vital information. You simply put your SIM card into this device, follow the simple directions and have a backup SIM card ready. This is handy not just if your cell phone is stolen but also if you decide to change your SIM card and get a new one.

Answer--

A SIM card or Subscriber Identity Module is a portable memory chip used in some models of cellular telephones. The SIM card makes it easy to switch to a new phone by simply sliding the SIM out of the old phone and into the new one. The SIM holds personal identity information, cell phone number, phone book, text messages and other data. It can be thought of as a mini hard disk that automatically activates the phone into which it is inserted.

A SIM card can come in very handy. For example, let's say your phone runs out of battery power at a friend's house. Assuming you both have SIM-based phones, you can remove the SIM card from your phone and slide it into your friend's phone to make your call. Your carrier processes the call as if it were made from your phone, so it won't count against your friend's minutes.

If you upgrade your phone there's no hassle involved. The SIM card is all you need. Just slide it into the new phone and you're good to go. You can even keep multiple phones for different purposes. An inexpensive phone in the glove compartment, for example, for emergency use, one phone for work and another for home. Just slide your SIM card into whatever phone you wish to use.

High-end cell phones can be very attractive and somewhat pricey. If you invest in an expensive phone you might want to keep it awhile. Using a SIM card, it is even possible to switch carriers and continue to use the same phone. The new carrier will simply issue you their own SIM card. The phone must be unlocked, however, and operate on the new carrier's frequency or band.

A SIM card provides an even bigger advantage for international travelers -- simply take your phone with you and buy a local SIM card with minutes. For example, a traveler from the U.S. staying in the U.K. can purchase a SIM card across the pond. Now the phone can be used to call throughout England without paying international roaming charges from the carrier back home.

SIM cards are used with carriers that operate on the Global System for Mobile Communication (GSM) network. The competing network is Code Division Multiple Access (CDMA), a technology created by U.S. company Qualcomm. As of fall 2005, CDMA cell phones and CDMA carriers do not support SIM cards in most parts of the world, though this is changing. A CDMA SIM card called the R-UIM (Re-Useable Identification Module) was made available in China in 2002, and will eventually be available worldwide. Expectations for the future include a cell phone market that supports both SIM (GSM) and R-UIM (CDMA) cards by default.

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First answer by Mani rathinam. Last edit by Rms2000. Contributor trust: 5 [recommend contributor]. Question popularity: 184 [recommend question].