A faulty SIM card can prevent your smartphone from connecting to a mobile network. Assessing whether you're experiencing bad SIM card symptoms or your smartphone is malfunctioning requires you to insert the SIM card in a different phone.
Check Your SIM Card
A few distinct issues can cause your smartphone to display a warning that it cannot access the SIM card. First, be aware that there are three different SIM card formats in use today: mini, micro and nano. Before attempting to insert the SIM card into a phone, check whether the device uses the same format as the card you want to test. For example, while most Android smartphones use SIM cards in the micro format, recent iPhones only support nano cards.
Verizon Wireless also recommends checking for a misaligned SIM card when you're having trouble connecting to the network. The shock of impact, such as when you drop your phone, can cause your SIM card to move in its slot and prevent your device from reading the embedded chip. To test whether your SIM card is misaligned, turn off your device and remove the SIM card. Reinsert the SIM card and turn your smartphone back on. If the SIM card was misaligned, your device should now be able to read the SIM card and connect to a mobile network.
The problem could also be a damaged SIM card or a malfunctioning smartphone. Checking whether your SIM card or your smartphone is to blame for your connectivity issues requires access to another smartphone, one you know is working properly. If you cannot find an alternate phone to test your SIM card, bring the card to your carrier's store since they often have some test SIM cards to use. Turn your smartphone off and remove the SIM card. Insert the card into the alternate smartphone. If the second phone is also unable to read the card, your SIM card is to blame for your issues -- either because it is dirty or damaged.
Clean Your SIM Card
Boost Mobile warns that a dirty SIM card can prevent your phone from reading the embedded data and connecting to a network. To clean a SIM card, rub the embedded chip with a soft eraser or the tip of a Gold Guard pen. After cleaning the card, insert it in the smartphone again and check whether your device can now access the chip's contents.
Damaged SIM Card Replacement
If -- despite cleaning the chip -- your phone is still unable to read the SIM card, you might have a faulty SIM card. To order a replacement SIM from your smartphone carrier, either visit one of your carrier's stores or contact its customer service department by phone or via the company's website.