BluetoothLE between apps has never been easier - Enter BLE Hubs
Two phones in the same room, no server, no Wi-Fi, and nothing but Bluetooth between them. That should be easy, and it has never been. So I took the SignalR hub model and put it on the radio: one C# interface, generated proxies, request/response, streaming, events, groups and JSON, with every byte chunked, framed and reassembled for you.