"Outgoing sound (internal and optional mic) drops out on iPhone 4"에 답변Above is all hold supported and true, your iphone is facing terminal failure due to bad audio ic. My recommended way is to remove the back cover, heat up the audio IC area while in a speakerphone call untill you hear sound. For 10 seconds of sound, quickly blow the area with canned air and cool it down. Voila you have it worked better for longer until it recurs again. You can do that for a few times until total failure. Thanks and good luck.