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 not. Hope it helps Chase.