iPhone 5c keeps dropping the first call I receive

Ok this is weird.

My iphone 5c was working great. And now for the past 2 months this thing happens 8 out of 10 calls i receive/make.

This is what happens:

I make/receive a call. I speak for about 30 seconds to 1 minute and then the call is dropped. Immediately I redial or I receive the same call and then the line is without problems, and doesnt drop. So in short the first time I receive or I make a call the line is dropped and if I call back immediately everything is ok.

Now I spoken with my carrier and everything seems to be alright on their part. I check the sim card into another phone and everything works fine. So it is my device.

This is driving me crazy. I have restarted the phone, there was even the update of 7.1.1 and nothing seems to fix this.

Do you guys have any ideas about this?

 

I see some people saying to call Apple and get it replaced. While that might be easy for some people next to an Apple store, I dont have this option. In fact in my country there is no Apple store.

So I have to ask, is this a known problem that is hardware related? Or is this a software thing?

To throw in some more information, I have on my phone a skinomi full body protector screen but I have this for 6 months now without any problems. So it cant be the one interferring.

I was pretty sure that this is a software issue as I said this happens only the first time i receive a call. But now I am worried by some replies.

By doing a clean restore, is there a way to keep my sms messages and such?