Fixed: I tried many of the suggestions that I found online (sim card, SD card, reset, load new firmware, etc) to fix my son's S4 - none of these suggestions fixed the problem. The mic, ear peace, and speaker all work fine sing VOIP dialers, I felt that the issue had something to do with the firmware (BIOS) or software. Since I had already reloaded the firmware, I factory reset the phone. During the factory setup process, I decided to log into the phone using my own Google account and restore my applications. This solved the problem. I hope this information helps others. Good luck!