I replaced the cracked screens of mine and my daughters 3gs iphone. My daughters phone worked perfectly once the job was done. All functions on my own hone also worked perfectly. However when i made or received a call the otherparty heard me ok but I could only hear them if i used speaker phone function or my headphones.
I read this post and re-opened my phone and low and behold the ribbon inside labelled 3 had come loose!!. What a great find . My iphone 3 now fuctions just as it should I can hear calls as normal. i was at a loss before I found this post. Thank you.
So if you have replaced your screen and can only hear your calls through the headset or speaker phone and all other sounds are ok , re open your phone and re fix the 3 connector it will have come loose !! hooray Good luck Donna