Who I have the same questioned this topic

Phone:  Verizon Samsung Galaxy S4 - Model SCH-I545 - Android Version: 4.4.2  Baseband version: I545VRUFNK1

Symptoms:  When placing a call or receiving a call, I cannot hear the other caller, and they cannot hear me.  Other caller can hear my dialpad keypresses, but I cannot hear their dialpad keypresses.  I am able to place calls and receive calls, but no audio.

When:  Started as an intermittent problem about 5 days ago, yesterday and today (2015-01-26) was consistently a problem.

What I've done:  Tried phone restart, soft reset, checked "OK, Google" settings, various other suggestions.  Finally today I did a factory reset.

After the factory reset today, the audio problem still existed.  After a few hours I called my phone from another cell phone, and everything worked.  Made several more incoming and outgoing test calls (voice mail, etc) and everything was working fine for about an hour.  Then audio problem reoccured and the audio has not worked since.  Around the (brief) time that it was working today, I had not made any changes to the phone. 

Since it stopped working today, I've done the following:

- Deleted all 3rd party apps

- Uninstalled all updates on stock (non-removable) apps

- Re-updated all apps

- Disabled "OK Google" setting

- Switched SIM cards with my wife's phone (audio not an issue with my SIM card in my wife's phone, so it seems to be a device problem, not a SIM card problem...)

- Used headphones

- Used speakerphone

After each of the above things, it did not fix my problem.  When dialing out, I can hear the connection beep in the phone speaker and in the headphones, but no voice audio.  The microphone works fine with other apps (text messaging, etc.).  So I've determined that the speaker and the microphone are operational.  I can receive and answer calls (but again, no audio)  When I'm connected with another caller, they can hear the tones if I press on the dialpad numbers, but I cannot hear tones if they press on their dialpad numbers.  

The only thing I have not tried is a BlueTooth headset.  I have had Bluetooth turned off the entire time.

Essentially the phone works as expected except for no audio on calls.  Internet, text messaging, email, Google voice search, etc are all working normally.

Any suggestions?  Several other posts with the same issue, but mine is not resolved with a factory reset....

Thanks for your input