Chosen Solution
My iPhone cannot detect sim card
Just in case this still matters. The most reliable fix for this issue is to simply remove your SIM card, clean it lightly using a dry cloth, ensure that there is no debris in the SIM slot, then reinsert the card, ensuring a snug fit. Other users have reported that briefly turning on Airplane mode (in Settings) then turning it back off can resolve the problem. Also, you might want to try to get a new sim card from your service provider….good luck:)
if you pop off the screen, check if the bottom brass arm is being moved when you slip in the sim card. If this doesnt move to disconnect from continuity, the phone doesnt know there is a sim installed.
Try cleaning the contacts on the iPhone and the sim card. -Me-
I had a similar issue, check this link for the fix :) Sim Reader faulty, short circut?
My iPhone sim not installed
Hard restart your phone i.e holding power and home button
