There are some good ideas on utube for repairs of this problem. I have exactly the same problem--I can hear the caller, but they can only hear me part of the time. I am waiting for some tools to come in the mail and then I am going to try the repair idea from youtube. the name of the video is: How to fix the iPhone 4 (4s) Mic problem and it's by rdesrets there are a bunch of other ideas on you tube too, but this repair seems to make sense.
