My phone says no sim installed, it is a 4S and it has been working up to now?? Help
I'd try turning it off and removing and reinserting the SIM. It may not have been installed tightly in the first place and may need to be reseated.
remove the sim and reinstall it. if that does not work go to your local AT&T store and ask for a replacement. my sim card this and it died i had to go to AT&T got FREE replacement sim card.
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