How does Dingtone turn my phone into a Walkie-Talkie (Push to Talk, or PTT)?

If both you and your contact are active on Dingtone, you have the option to push a button to talk. Your friend will immediately hear you and he can reply to you by pushing the same button in his Dingtone app…just like a real Walkie Talkie.

The Dingtone Walkie Talkie even works after you lock your phone.