Making A Chat System

Hi there! Basically what I am trying to do is make a multiplayer chat system using Remote Procedure Calls. My code doesn't seem to be adding the new line (updating that chat) at all. Here is my code: using UnityEngine; using System.Collections;

 public class Player : MonoBehaviour
 {
     public float speed = 10f;
 
     private float lastSynchronizationTime = 0f;
     private float syncDelay = 0f;
     private float syncTime = 0f;
     private Vector3 syncStartPosition = Vector3.zero;
     private Vector3 syncEndPosition = Vector3.zero;
     private string str = null;
     private string talk = null;
 
     void OnSerializeNetworkView(BitStream stream, NetworkMessageInfo info)
     {
         Vector3 syncPosition = Vector3.zero;
         Vector3 syncVelocity = Vector3.zero;
         if (stream.isWriting)
         {
             syncPosition = rigidbody.position;
             stream.Serialize(ref syncPosition);
 
             syncPosition = rigidbody.velocity;
             stream.Serialize(ref syncVelocity);
         }
         else
         {
             stream.Serialize(ref syncPosition);
             stream.Serialize(ref syncVelocity);
 
             syncTime = 0f;
             syncDelay = Time.time - lastSynchronizationTime;
             lastSynchronizationTime = Time.time;
 
             syncEndPosition = syncPosition + syncVelocity * syncDelay;
             syncStartPosition = rigidbody.position;
         }
     }
 
     void Awake()
     {
         lastSynchronizationTime = Time.time;
         str = "-=-=- Messages will appear here -=-=-\n";
         talk = "Chat";
     }
 
     void Update()
     {
         if (networkView.isMine)
         {
             InputMovement();
             InputColorChange();
 
 
         }
         else
         {
             SyncedMovement();
 
         }
         if (rigidbody.position.y < -10) {
             str = str + "Someone fell out of the world.\n";
             rigidbody.position = new Vector3(0,5,0);
         }
     }
 
 
     private void InputMovement()
     {
         if (Input.GetKey(KeyCode.W))
             rigidbody.MovePosition(rigidbody.position + Vector3.forward * speed * Time.deltaTime);
 
         if (Input.GetKey(KeyCode.S))
             rigidbody.MovePosition(rigidbody.position - Vector3.forward * speed * Time.deltaTime);
 
         if (Input.GetKey(KeyCode.D))
             rigidbody.MovePosition(rigidbody.position + Vector3.right * speed * Time.deltaTime);
 
         if (Input.GetKey(KeyCode.A))
             rigidbody.MovePosition(rigidbody.position - Vector3.right * speed * Time.deltaTime);
 
         if (Input.GetKey(KeyCode.Space))
             rigidbody.MovePosition(rigidbody.position + Vector3.up * 5f * Time.deltaTime);
     }
 
     private void SyncedMovement()
     {
         syncTime += Time.deltaTime;
 
         rigidbody.position = Vector3.Lerp(syncStartPosition, syncEndPosition, syncTime / syncDelay);
     }
 
 
     private void InputColorChange()
     {
         if (Input.GetKeyDown(KeyCode.R))
             ChangeColorTo(new Vector3(Random.Range(0f, 1f), Random.Range(0f, 1f), Random.Range(0f, 1f)));
     }
 
     [RPC] void ChangeColorTo(Vector3 color)
     {
         renderer.material.color = new Color(color.x, color.y, color.z, 1f);
 
         if (networkView.isMine)
             networkView.RPC("ChangeColorTo", RPCMode.OthersBuffered, color);
     }
     void OnGUI()
     {
         if (Event.current.type == EventType.KeyDown && Event.current.keyCode == KeyCode.Return) {
             if (talk.Equals ("/cls")) {
                 str = "";
                 talk = "";
             } else {
                 if (talk != null){
                     str = str + talk + "\n";
                     talk = "";
                     Chat (str);
                 }
             }
         }
         if (networkView.isMine) {
             GUILayout.Label (str);
             talk = GUI.TextField (new Rect (500, 0, 400, 20), talk);
         }
 
     }
     [RPC] void Chat(string msg){
         str = msg;
 
         if (networkView.isMine) {
             networkView.RPC("Chat", RPCMode.OthersBuffered, msg);
         }
     }
     
 }

Thanks for any help!