The app itself is already available in beta on Android. It is an ethereum client for mobile, and it includes a messenger that uses whisper, a gossip protocol to transmit data (at least for now), which provides darkness and encryption.
The first iteration of Tribute to Talk will be pretty basic with a simple transactional model. A pays B to start talking to B, B can block A at any time. But the smart contract developers are working on more sophisticated schemes for the future.
