iPhone Text Box Not Working

Ok so im trying to make a textbox that you can put text in (duh) but the problem is the text will only stay for not even a second and dissapear. Here is my code.

 private var keyboard : iPhoneKeyboard; 

 function OnGUI() {
 
    username = GUI.TextArea(Rect(600,300,200,50),"",200);
 
 if(keyboard) {
     username = keyboard.text;
 }    
     
 if (GUI.Button (Rect (600,160,120,120), "Submit Score")) {
     postScore(username,blackHole.MyScoreCounter);
     
 }

}

I am using the unity wiki site to create a highscore for my game and i just want to use a textbox to use for the username.