Based on http://forum.unity3d.com/threads/c-tcp-ip-socket-how-to-receive-from-server.227259/

UnitySocketExample.cs

using UnityEngine;
using System.Collections;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.Text;

public class HelloSocketWorld : MonoBehaviour {
	public string history;
	public string txt;

	private byte[] _recieveBuffer = new byte[8142];

	// Use this for initialization
	void Start () {
		clientSocket = new Socket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);
		clientSocket.Connect(new IPEndPoint(IPAddress.Loopback,port));

		clientSocket.BeginReceive(_recieveBuffer,0,_recieveBuffer.Length,SocketFlags.None,new System.AsyncCallback(ReceiveCallback),null);


		history = history + "\nServer Connected ...";
	}

	private void ReceiveCallback(System.IAsyncResult AR){
		//Check how much bytes are recieved and call EndRecieve to finalize handshake
		int recieved = clientSocket.EndReceive(AR);

		if(recieved <= 0)
			return;

		//Copy the recieved data into new buffer , to avoid null bytes
		byte[] recData = new byte[recieved];
		System.Buffer.BlockCopy(_recieveBuffer,0,recData,0,recieved);

		//Process data here the way you want , all your bytes will be stored in recData
		var dataFromClient = System.Text.Encoding.ASCII.GetString(
			recData, 0, recData.Length);

		history += dataFromClient;

		//Start receiving again
		clientSocket.BeginReceive(_recieveBuffer,0,_recieveBuffer.Length,SocketFlags.None,new System.AsyncCallback(ReceiveCallback),null);

	}

	// Update is called once per frame
	void Update () {
		
	}

	// The port number for the remote device.
	private const int port = 5000;

	private Socket clientSocket = new Socket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);

	NetworkStream serverStream;

	private void SendData(byte[] data)
	{
		SocketAsyncEventArgs socketAsyncData = new SocketAsyncEventArgs();
		socketAsyncData.SetBuffer(data,0,data.Length);
		clientSocket.SendAsync(socketAsyncData);
	}

	void OnGUI(){
		history = GUI.TextField (new Rect (0, 0, 200, 300), history);
		txt = GUI.TextField (new Rect (0, 300, 200, 50), txt);

		if (GUI.Button(new Rect(0,350,0200,50),"Send")){
			byte[] outStream = System.Text.Encoding.ASCII.GetBytes(txt);
			SendData (outStream);

			history += "\nMe: " + txt;

			txt = "";
		}

	}
}