IPhone 4 sim card problem...?

Hi, If the sim has been working fine then it doesn't seem that that is the problem. Was it just this 1 call? Have you tried other calls? Occasionally in a call your cheek will press the mute on. I have done this a few times even though Apple say they fixed this in the last update. If it happens again move the phone away from your ear and you will see if the mute on has turned blue. If it has just press it to un mute it. ♥