Unable to make calls on Iphone 4

I've never had a problem with my iPhone 4 until a few days ago. Whenever I make a phone call all i hear is a crackling noise… Sometimes I won't hear anything at all. No ringing sound, no static noise, nothing. I have no idea why this happened but i'm unable to make/receive phone calls. I also made this youtube video to show you what is going on:

+Also, the speakers work. Other than this problem the iphone is in perfect condition.

Turn the phone completely off and after two minutes turn it back on… How long have you had it and are you warranty… Have you had it near water or any other fluid? Talked on the phone in the rain or even leave it sitting in your bathroom while your showering? Because all that takes effect… Steam, humidity all that will mess with the phones, the other thing is depending on whose your carrier, if its AT&T get a new SIM card… If its another provider ask them to refresh your signal base… If none of that works… Go to apple, they will figure it out