I had a similar (if not the same) problem. I found that when I used some earphones with the earphone jack and then removed the earphone plug from the jack, the sound only came from the phone speaker and was thus very quiet no matter what I tried with audio settings. Both times happened when I plugged in external earphones in the jack. Both times had the unit remain in the phone speaker mode until I power cycled it and it returned to normal in both cases. I don't know if there is a less obtrusive way to get the audio back to the regular speaker but this seems like a "feature" that ought to be fixed in an OTA update such as the one that is imminent.