SIM card means Subscriber Identity Module which is a small circuit board. Actually SIMcard is placed in your GSM phone in order to identify it to your carrier.
You can swap SIMs in GSM phones and your phone number, voice, and data plans are swapped right along with the help of SIM card. A SIM card is usually identified by its Integrated circuit card identifier that is engraved on the body of the card of a SIM. Actually they are also identified by the carrier from its International mobile subscriber identity (IMSI).
How to use SIM card?
There are many uses of a SIM card. The main benefit of a SIM is that you can easily swap phones [...]