SIM cards are 2.5 by 1.5cm in size. In almost every mobile, they slide into a special slot behind the battery. Most have a slide or clip to keep them firmly in place. Switch the handset off Carefully snap out the gold-colored SIM card from the plastic card. 
Remove the back cover of the phone by pressing the release button and remove the cover off the phone. (see example 1 & 2 below) Remove the battery from the phone. Once you remove the battery the SIM holder will be exposed. Open the SIM card holder or compartment. Use a fingernail as a lever to unlatch the metal or plastic SIM card holder. Place the SIM card into the SIM holder with the gold square facing down. Gently swing or close the SIM card holder until it clicks into place. Note: The smart card and its contacts can easily be damaged by scratches or bending, so be careful when handling, inserting, or removing the card. Place the battery and the battery cover back on the phone. if the SIM card is inserted incorrectly or is damaged. The "Insert SIM card" or "Check SIM" message will appear on the display when the phone is turned on. Remove the SIM card and re-insert as instructed above. Keep all SIM cards out of reach of small children.  Example 2: 
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