IPHONE 4GS no SIM rilevata e fisso in "Cerco..."
After changing the screen on iPhone 4S with iOS6 starts this problem.
The solution I found: Insert the sim before you turn on the phone. Then connect the iPhone to the WiFi. Take the sim card out, and put if back in ;)
Hopefully this will resolve the problem. Worked for me all three times :)
I think the reason this might work is that it change the time and date to normal...
If you use iOS 6 try to set the correct time in settings and reboot before inserting SIM card.
Unless you have physically damaged the phone, as in knocked the signal resistor or the blue coil off the board etc, I have found that if you turn the phone off, insert the SIM card, turn the phone on, go to settings and connect to wifi, return to the home screen, pop out the sim card, it should now recognise the SIM card by saying "no SIM card installed" put the card back in and it should pick up signal after a minute. It seems to be an iOS 6/6.0.1 glitch, or maybe something Apple put in to irritate independent repairers like myself. This works for me more often than no