A SIM card in a cell phone or smart phone is a small plastic card with circuits on it. This card holds the user's account information, which allows the cell phone service network to find and connect to the phone. It also contains the user's directory and such other stored data as photos, files and text messages. A rejected SIM card will cause the phone to malfunction. This can occur if the card is damaged, wet, dirty or dislodged.
Locate the SIM card on the phone. Generally the card is stored under the battery. You'll probably have to remove the back cover before you can slide out the battery. Be sure the phone is turned off before doing this.
Remove the battery and look for the SIM card. It is usually white or yellow with circuitry printed on it. Sometimes it has text on it as well. The card may be as small as a thumbnail.
Remove the SIM card, which is usually held in place by a metal clip. To unlock the clip, lift it up or slide it up or down. Gently lift or slide the SIM card up and out of the clip. You may need a pair of tweezers.
Blow around the area where the SIM card had been lodged to disperse any dirt or dust.
Look for any water, dirt or grime that may have gotten into the phone or on the SIM card. Use a soft cloth to gently wipe the SIM card, the battery and the area around the SIM card compartment. Make sure to use a fine cloth that will not tear or catch on circuitry and other metal parts.
Inspect the SIM card for damage such as cracks. If the SIM card appears undamaged, firmly return it to its home in the clip. The SIM card circuitry should be face down so that it is touching the metal connectors on the phone. Slide the clip back into place to secure the SIM card.
Replace the battery and any casing. Turn the phone on. If the SIM card has been cleaned and properly placed back into the phone, it should function properly.
Contact your cell phone service provider if the SIM card is still rejected. You may need to replace it.