Hearing an echo of my voice using the Apple headset I'm not sure if it occurred after I upgraded my iPhone 4 to iOS 6 but since some days I hear an echo of my voice when using the Apple headset on phone calls. It also seems that when I simply plug in the headset without calling or listening to music I hear some noise trough the earphones.

The echo is very annoying and it's almost impossible to use the headset for phone calls. Is there any solution or are there any other problem descriptions?
I am having the same exact issue. I have called Apple Care and all they could tell me was to do a soft reset, and a full restore and that the cause would be hardware related. I don't believe it's hardware related since this occurred after the upgrade to iOS 6 so this is clearly a software related problem. They made no other suggestions on how to resolve this issue at this time. 

I did however google this and found this post.

This seems to have been an issue even with iOS 5 on the 4S. This only happens when plugging the headset in during a call. If you initiate the call with the headset already plugged in the echo is not there. If you plug the headset in during a call however, in order to get rid of the echo, turn the speaker on and off (with the headset still plugged in) and the echo will go away.