iPhone 4S having audio issues - Other side hears his echo during call My uncle bought a brand new iPhone 4S last week and it is suffering from an annoying problem, side b (not him) hears himself with echo. The error does not occur while
using headset or speakerphone, only when using handset.

Is there a fix for that problem?

iPhone 4S
Version 5.1
I had this exact problem with a 4S until today. Here is what I did:

I installed Skype and Google Hangouts on the 4S to check whether this problem occurs with any calling application or just GSM. I made calls with Skype and Hangouts via WiFi and had no problem at all.

So I had a friend with a 4S with no such problems and I borrowed his SIM card for a test. I called his number on my 4S and had no echo problems! I put mine back and the echo returned. To make sure, I repeated this a couple of times. My SIM had echo, his no echo.

So I went to my provider's shop and requested a new SIM. Problem gone.

I hope this helps people who have tried all else with no results.  Why the SIM caused this is beyond me.