I replaced the back of my iPhone 3G 16 Gb and carefully reconnected all the cables, but now i get no sound from the bottom speaker. headphones, sync and microphone all work fine. phone even shows separate volume indicators for headphone and internal speaker, so i think the headphone jack is switching appropriately. at first the vibrate function was not working as well, but i reopened it and bent up the connectors on the vibration unit and now it works. basically, just no sound for ringtone, text msg, iPod, speakerphone. help!