what is a SIM card?

meems

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Dec 3, 2008
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#1
Pls excuse my ignorance on this. I've seen a lot of posts mentioning SIM cards and it dawned on me that I don't really know what that is. This is the 1st phone I've had that had one (to my knowledge). What does a SIM card do?
 

kenneth

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Aug 19, 2008
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#2
A sim card is a card that is inserted into the phone to activate it. It looks like a sd card for a computer.
 

kenneth

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#3
On the iPhone it is located between the headphone jack and the power button. There is a small hole that you push in the simbremoval tool and a tray will pop out and expose the sim card. Only certain networks have them like t-mobile, AT&T, and I'm not sure about any others.
 

Marianne

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Jul 16, 2007
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#4
See this.

SIM stands for Subscriber Identity Module. It holds your phone number (and tells whatever phone you're using what it is) and is the most critical part of your phone to get it to connect to your cellular network so you can make and receive calls. As Kenneth said, only certain networks use them - Sprint and Verizon do not (these are CDMA networks), for the most part, though I think they are pretty much required on GSM networks...
 

kdarling

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#11
In addition to the above... a SIM card is a microcomputer.

It has an ARM or other cpu with some RAM for running programs and sometimes up to 64MB of Flash memory for program and data storage.

There is a standard for another CPU to talk to the SIM, so phones don't have to know the SIM's internal workings.

Usually you can store contacts info on a SIM, so it moves with you from phone to phone. Alas, the iPhone will only allow importing contacts from a SIM.

Some SIMs can even run Java programs, so you can also carry your favorite small applications or games with you.

3G SIMs are different from 2G and previous SIMs, in that they have special commands and hardware for more secure authentication and encyrption calculations.