I have an iPhone 2G (1st gen) that I recently repaired and everything works great except the sound. The sound will only play through the speaker if the headset is plugged in and it will not play through the headset at all. I've tried everything I could possible think of including trying to mess around with the contact switch inside the headphone jack, restoring the iPhone to various firmware releases, jailbroken and not. Nothing has worked and I'm about to pull my friggin hair out! Someone please help me!
This happened to me before. I ended up replacing the entire headphone jack ribbon assembly that's attached to the back panel. It worked properly for me afterwards.