As of v3.5, this function is no longer available.
Map external hardware buttons
1. Use your iPhone/iPod/iPhone wired headset.
Enable "Headset/remote control" and change the push to talk action to "Toggle mode" to use the buttons on your apple headset to PTT in the foreground and the background.
2. Zello certified devices for true push to talk mode
To see a list of devices you can use as true push to talk, please see Zello compatible devices.