For new multiplayer social game I created simple TCP client as Android application. It connects to special echo server (.NET) and sends/receives packets to/from other clients. Packets are UTF-8 text messages prefixed by string length 4-bytes integer as a header of the packet.
I used Java NIO to implement network layer with second worker thread to wait for connection establishment and further reading of incoming packets. Network layer is separated of GUI, so, ready to be used in other Android application. Eclipse project, .NET server and client for tests are here.