okay, so i have my my 3rd handset (4s 64GB) and it still has the same echo problems. i have tried restoring, restoring from backup and all the rest. i have just got off the phone from apple care, currenltly they are organising a new iphone from the factory to try and reduce the chance that it was just a bad batch that was sent through. but for the weekend he wants me to makes notes how often it happens. Mostly because this is an intermittent problem which is the worst thing to troubleshoot, and very hard to pin point but only eliminate
But among the three handsets i have had this is what i have tried - which did not effect the echo or change the occurance rate.
restore the phone to factory
restore to a backup
restore to an earlier backup
different headset, i took one out of the packet and used only on the new phone. no change.
turning wi-fi off. i thought something about the new antenna switching could be the cause. nope.
turning bluetooth off. no change.
tried a diffferent sim card, tommorow i will be replacing the sim card just to completely eliminate the question.
changing options with siri.
it is clear so far that it is not a carrier issue (or any difference between CDMA and GSM), it is not a proximity issue. Currently there are a few strong possibilies, such as Siri could be changing the way the microphone is used and incorrectly feeds the signal back through the call or perhaps it is just a launch hardware issue (decreasing in chance though). I personally believe it is a software issue and related to some part of the noise cancellation that is meant to run in the background.
TLDR: now using a 3rd handset, apple still doesn't know anything, wants to replace it again but make notes about the echo until the new phone comes.