I have a 4S and its a strange issue, it doesn't recognise any SIM card 99% of the time. By this i mean tonight i have removed the board and using compressed air and pure alcohol cleaning solution to try and clean the SIM area and it worked!, right up until i removed the SIM card to try another. Before i did this i had nothing recognised.
I don't know if i should try a different SIM reader, my abilities don't stretch that far so will have to pay. I'm more concerned it could be an issue on the board as the SIM reader looks perfectly fine.