1. To turn AT&T HD Voice on or off, swipe down from the top of the screen, then tap the Settings icon.
   Note: To use AT&T HD Voice, both caller and receiver need an AT&T HD Voice-capable phone and must be located in an AT&T HD Voice coverage area.
   
2. Under the Network connections section, tap More networks.
   
3. Tap Mobile networks. 
   
4. Tap Mobile data.
   
5. Tap the Enhanced LTE Services checkbox to turn AT&T HD Voice on or off.
   Note: Turning AT&T HD Voice off will also disable AT&T Video Call and Advanced Messaging. Learn more about AT&T HD Voice.