Here's a javascript solution:

/* 

*  This file is part of the Unity networking tutorial by M2H ([url]http://www.M2H.nl[/url])

*  The original author of this code is Mike Hergaarden, even though some small parts 

*  are copied from the Unity tutorials/manuals.

*  Feel free to use this code for your own projects, drop us a line if you made something exciting! 

*/

#pragma strict





public static var usingChat : boolean = false;  //Can be used to determine if we need to stop player movement since we're chatting

var skin : GUISkin;                     //Skin

static var showChat : boolean= false;           //Show/Hide the chat



//Private vars used by the script

private var inputField : String= "";



private var scrollPosition : Vector2;

private var width : int= 190;

private var height : int= 180;

private var playerName : String;

private var lastUnfocus : float =0;

private var window : Rect;

private var lastEntry : float = 0.0;

private var netView : NetworkView;

private static var thisScript : FPSChat;



private var chatEntries = new ArrayList();

class FPSChatEntry

{

    var name : String= "";

    var text : String= "";  

}





function Awake(){

    usingChat=false;



    netView = networkView;

    thisScript = this;



    window = Rect(Screen.width-185, 20 + scoreBoard.scoreBoardHeight, width, height);

    lastEntry = Time.time;



    playerName = PlayerPrefs.GetString("playerName", "");

    if(!playerName || playerName==""){

        playerName = "RandomName"+Random.Range(1,999);

    }   

}



function CloseChatWindow ()

{

    showChat = false;

    inputField = "";

    chatEntries = new ArrayList();

}



function ShowChatWindow ()

{

    showChat = true;

    inputField = "";

    chatEntries = new ArrayList();

}



function OnGUI ()

{

    if(!showChat){

        return;

    }



    if (PlayerInfos.ScreenState() && PlayerInfos.IsUsingStore()){

        return;

    }



    GUI.skin = skin;



    window.y = 20 + scoreBoard.scoreBoardHeight;



    if (Event.current.type == EventType.keyDown && Event.current.character == "\n" && inputField.Length <= 0)

    {

        if(lastUnfocus+0.25<Time.time){

            usingChat=true;

            GUI.FocusWindow(5);

            GUI.FocusControl("Chat input field");

            Screen.lockCursor = false;

        }

    }

    if (Time.time - lastEntry > 10 && Network.isServer){

        addGameChatMessage(" ");

        lastEntry = Time.time;

    }



    //Screen.lockCursor = screenLock;

    window = GUI.Window (5, window, GlobalChatWindow, "");

}





function GlobalChatWindow (id : int) {



    GUILayout.BeginVertical();

    GUILayout.Space(10);

    GUILayout.EndVertical();



    // Begin a scroll view. All rects are calculated automatically - 

    // it will use up any available screen space and make sure contents flow correctly.

    // This is kept small with the last two parameters to force scrollbars to appear.

    scrollPosition = GUILayout.BeginScrollView (scrollPosition);



    for (var entry : FPSChatEntry in chatEntries)

    {

        GUILayout.BeginHorizontal();

        if(entry.name==""){//Game message

            GUILayout.Label (entry.text);

        }else{

            GUILayout.Label (entry.name+": "+entry.text);

        }

        GUILayout.EndHorizontal();

        GUILayout.Space(3);



    }

    // End the scrollview we began above.

    GUILayout.EndScrollView ();



    if (Event.current.type == EventType.keyDown && Event.current.character == "\n" && inputField.Length > 0)

    {

        HitEnter(inputField);

    }

    else if (Event.current.type == EventType.keyDown && Event.current.character == "\n" && inputField.Length == 0){

        inputField = ""; //Clear line

        GUI.UnfocusWindow ();//Deselect chat

        lastUnfocus=Time.time;

        usingChat=false;

        Screen.lockCursor = true;

    }

    GUI.SetNextControlName("Chat input field");

    inputField = GUILayout.TextField(inputField);





    if(Input.GetKeyDown("mouse 0")){

        if(usingChat){

            usingChat=false;

            GUI.UnfocusWindow ();//Deselect chat

            lastUnfocus=Time.time;

        }

    }

    //if (Screen.lockCursor == false){

        //if(usingChat){

            //usingChat=false;

            //GUI.UnfocusWindow ();//Deselect chat

            //lastUnfocus=Time.time;

        //}

    //}

}



function HitEnter(msg : String){

    msg = msg.Replace("\n", "");

    netView.RPC("ApplyGlobalChatText", RPCMode.All, playerName, msg);

    inputField = ""; //Clear line

    GUI.UnfocusWindow ();//Deselect chat

    lastUnfocus=Time.time;

    usingChat=false;

    Screen.lockCursor = true;

}



static function StaticMsg(msg : String){

    thisScript.HitEnter(msg);

}





@RPC

function ApplyGlobalChatText (name : String, msg : String)

{

    var entry : FPSChatEntry = new FPSChatEntry();

    entry.name = name;

    entry.text = msg;



    chatEntries.Add(entry);

    lastEntry = Time.time;



    //Remove old entries

    if (chatEntries.Count > 4){

        chatEntries.RemoveAt(0);

    }



    scrollPosition.y = 1000000; 

}



//Add game messages etc

function addGameChatMessage(str : String){

    ApplyGlobalChatText("", str);

    if(Network.connections.length>0){

        networkView.RPC("ApplyGlobalChatText", RPCMode.Others, "", str);    

    }   

}

There is a nice tutorial to do something extremely similar in the M2H Networking tutorial available from the Asset Store. More detials here:

http://forum.unity3d.com/threads/75385-Ultimate-Unity-Networking-project-Add-multiplayer-to-your-game-today!

It costs a small price but is ultimately worth it since it teaches you what you need to know to add multiplayer/chat/networking to any game.