Zello can utilize one of the buttons on the Voyager to trigger PTT, when Zello is in the foreground or background. The back button works as PTT, and the button underneath the microphone replays the last message with a short press.

The button works as toggle mode only but requires no special set-up. Simply, pair with your Android device and make sure that Bluetooth is selected in the bottom corner in your talk screen.

Simply, press to start talking, and then press again to stop talking. 

If you want to stop using the Voyager as PTT headset, you can go to Options > Push to talk button> Deselect Handle wireless headset button.