The problem usually has to do with the copper connectors on the sim card getting dirty. ''' To fix it just follow the steps.'''
* 1 Pop out the sim card by putting a small paperclip or pin into the tiny hole on the side of your Phone. Push hard so it pops out.
* 2 Take the card out of the little tray. Remember how it looks when it was in so you can put back correctly.
* 3 Put some rubbing alcohol on the end of a Q-Tip.
* 4 Rub the copper side of the sim card thoroughly. Wait a minute to let it dry.
* 5 Stick the card back in the slot.
* 6 Problem should be solved.