What is happening is that she is accidently pressing the "up"
portion of the rocker switch on the left side of the phone when she flips the phone open.
You will notice (try this on purpose)that when you open the phone while holding the rocker switch up, that there are no key sounds when dialing a number. Oh yes, the number will dial and even show connected on the screen--but no sound!!!.
Now, to hear the dialed number ringing, you must press the speakerphone button below the rocker switch. You don't have to turn on the speaker phone, just pressing this button restores sound.
On the next call however, the sound will STILL not work until you press the 4 way toggle button in the center of the phone. Now the phone is restored to normal status.
It took me about five hours and a million combinations of buttons to figure this out. See my post, from 121212.