3GS Ear speaker doesn't work after replacing the screen glass - FIX
The speaker connection is cable #3, its the one with out a plug and is hidden under the two cables with plugs.
The cable slips into a tiny flat white plastic socket that doesn't look much like a socket. ON the back of the white socket is a small strip that is BLACK. Use something small to gently LIFT it from the back. It is hinged in its front, the side next to the white part. It takes no effort at all to pop it up.
Its job is to apply pressure to the top of the white plastic, forcing it and the connection strips to firmly contact the top of that cable connections. The YOU TUBE videos skip over the part of lifting that black hinge retainer and I believe it is the single spot that causes all the problems mentioned about the ear piece not working after replacing the glass and LCD.
Its easy to break one edge of the white part, just enough to cause that last contact to not have pressure on its cable counter part.
I did manage to chip off the right edge of mine and of course my speaker didn't work. But I did get it to work once by pressing on the outside of the case in that area which gave me the clue.
I fixed mine by putting some sticky foam tape bits over the connector once the cable was inserted and the black retainer hinge snapped down, I used two small bits of the foam mounting tape maybe cut the same shape as the white plastic, but favoring that right side where I broke the plastic bit away.
Being very careful to not dislodge the cable I put it back together and...it works.