I noticed that there are 7 pins located at the sim card connection location. 6 are used to make contact with the sim card and 1 is probably used to check if the sim card slot is locked correctly. If you bend up the 6 pins, also make sure you bend up the 7th very tiny pin. I am not saying it really solves the problem, but maybe some might be able to solve a problem caused by this very small 7th pin on the side of the sim card slot.