I have just picked up a second hand 3GS Iphone which was sold as being in tip top order (!). It does actually look almost perfect however when trying to make a call both the inbuilt mic and earpiece will not work. Using the external speaker you can hear the call but the mic still doesnt work. Using handsfree mic/earpieces everything works fine as does bluetooth handsfree. I have checked the earphone plug socket...it is clean with no obstruction, I have also tried a full restore with no change.
As far as I know the screen has not been off the phone.
Does anyone have any suggestions as to the next best step?