On my iPhone 4, people cant hear me when I make and / or receive normal (GSM) phone calls. But when on calls using internet based / native apps like viber or skype, people can hear me just fine. Voice memos work too and have already tried different SIMs

Question

On my iPhone 4, people cant hear me when I make and / or receive normal (GSM) phone calls. But when I make/receive calls using internet-based / native apps like viber or skype, people can hear me just fine. I have tried recording my voice using voice memos - this works. And have already tried different SIM cards but the problem persists.
I have taken my phone to an authorized Apple service center, where they restored my phone to factory settings, but still facing the same issue. They service center directed me to Apple Customer Care Hotline, where I have now spent 3+ hours explaining my issue and yet no one can resolve it. The easy answer if to replace the phone - and since it is out of warranty, I am expected to pay for it.
Additionally, the customer service has been so rude and confrontational that it has completely changed my view of Apple and its customer focus. I am a disappointed and angry customer today - people would be surprised to hear just how rude customer service was including making statements such as "Apple doesnt make infallible products, that's why warranty is needed for our products" and that "every product undergoes a problem at some stage, so do ours!" There goes whatever confidence I had...
My concern is simple - if no one at Apple and / or its CS hotline is able to address my issue comprhensively and keep telling me that they have never encountered a precedent before, then with what right can they expect me to pay for a replacement?! I am NOT here to fund Apple's research into their product faults and manufacturing.
And even though a customer is out of warranty, is it too much to expect an Apple product to work well for at least a 'reasonable' period of time. My phone is less than 18 months old and has been facing this issue for the past 2 months - surely the longevity of Apple products is more than 18 months!
Just a sad sad day for an Apple customer, compounded by unjustifiably rude and aggressive staff. And still no resolution to my problem.

Answer 1

I am having the same issue - with my last 2 iPhone 4's. My first handset each time I was on a call wether it was up to my ear or on loud speaker, the call would automatically mute even though the mute button wouldn't show up as highlighted. Pressing the mute button on and off during the call doesn't fix it either. I rang Apple and asked what some of their trouble shooting solutions were. I got told that it might be a software issue and to install the latest software update. This failed. I then got told to uninstall the software on the phone and do a complete restore. This also failed. After trying the troubleshooting suggestions, I took the phone into my provider and they sent me out a new phone within a week under warranty claiming it was a hardware issue and probably just a "glitch" with that particular phone. This was not the case....
After receiving my second iPhone 4, I was hopeful that it would work. For the first couple of days, making/receiving calls was not an issue. Until after about a week, the same problem started again. In one instance I had to hang up and call back 4 times and the call would still automatically mute after about 5 seconds. Also on the second handset, the main camera located on the back of the phone has red and blue lines running through it and can't take a decent picture. So back to the store I go to get another replacement - Again.
For a phone that is rated highly and as a keen Apple product purchaser, I am a bit disappointed with the experience I have had with the iPhone 4. Let's hope they find a fix sometime soon because this is becoming a bit beyond a joke.....!!