$(document).ready(function()
{
    $("#number").blur(function()
    {
        $("#msgbox").removeClass().addClass('messagebox').text('Checking').fadeIn("slow");
        //check the username exists ajax
        $.post("user_availability.php",{ user_name:$(this).val() } ,function(data)
        {
          if(data=="no") //if username not avaiable
          {
            $("#msgbox").fadeTo(200,0.1,function() //start fading the messagebox
            {
              $(this).html('<img src="img/off.png" alt="Number registered" />').addClass('messageboxerror').fadeTo(900,1);
            });
          }
          else
          {
            $("#msgbox").fadeTo(200,0.1,function()  //start fading the messagebox
            {
              $(this).html('<img src="img/on.png" alt="Number unregistered" />').addClass('messageboxok').fadeTo(900,1);
            });
          }

        });

    });
});