According to one iXBT.com user, if the smartphone does not “see” the SIM card, the first thing you should do is reboot the device. If the problem is not resolved after that, you should understand what is wrong and what is the problem: in the SIM card itself or in the phone.
Take a close look at the SIM card. If the gold-plated contacts are dirty, try to clean them gently with an eraser, and then wipe them with a special cloth. Also check the contacts of the receiver of the SIM card (of course, if they appear): if they are pressed or bent, try to straighten them with a thin needle.
If the SIM card is not detected due to problems with the smartphone, there are several options. The first is that the device itself can only work with SIM cards of certain operators (this happens when the device is brought from abroad). The second is flashing or updating software bugs. To fix this problem you will need to reset network settings or reset all data. In the second case, all files on the smartphone will be deleted.
If you have an Android device and want to reset network settings, you have to do it via “Settings”. Go to “General Settings”, then click “Reset” and then “Reset Network Settings”.
Also, the reason why the mobile does not “see” the SIM card may be that the SIM card slot is damaged or that all data is loaded for too long.
It also happens that the main problem is with the SIM card. If you don’t activate it (some carriers require you to do a paid action to activate) or it gets blocked (due to negative balance or because you don’t use it), the SIM card itself will be damaged. To fix all these problems, you need to contact the operator.
Source: Ferra
