Change the network setting to GSM from 3G on the phone if you haven't done so already and if that doesn't help then well....I'm guessing your sims defective or something o.O because of all the users this problem has rarely happened.
So try that first and then see what happens and go from there.
Ps. you don't need to post this two times and spam the sections -_-''
Contrary to popular belief I'm not really obsessed or in love with tofu as a food, sure its good and all but I'm not in love with it. Someone else typed this name for me when I was registering >_>
ps. For future reference just qoute me as Tofu instead of the whole name....sounds too cheesy LOL