[jQuery] $.getJSON does not call call back function

[standerby]

Hi,

I am trying to call a cross domain web service using the following
code. The return data is in XML format. It appears that the call back
function isn't get called. I can not add ?callback=? to the then of
the url. Any thought? Thanks.

 $.getJSON("http://www.webservicex.net/WeatherForecast.asmx/
GetWeatherByZipCode",
   {zipcode:"21234"},
   function(data){
    var idx = 0;
    $(data).find('WeatherData').each(function(){
      WeatherData[idx] = $(this).find('MaxTemperatureF').text();
      WeatherPicture[idx] = $(this).find('WeatherImage').text();
      idx++;
    }); //close each(
  });