JQuery :: Loading New Content When Scrolled To Bottom Of Page

I have built a site that loads new content from a database when the user hits the end of the page. This works fine in all desktop browsers and on the iPad, but is not working on the iPhone. Have tried an iPhone 3g and 4.

Here is the code:
$(window).scroll(function(){
if($(window).scrollTop() == $(document).height() - $(window).height()){
$.ajax({
type: 'POST',
url: 'nextSet.php',
data: "?dummy=" + new Date().getTime(),
dataType: 'html',
cache: false,
beforeSend: function() {
$('#scrollLoading').show();
$('#scrollLoading').html('<p><img src="/images/ajax-loader.gif" alt="loading..." /></p>');
},
success: function(response){
$('#scrollLoading').hide();
$('#resultsPageSearch p').css('margin','0');
$('#sortDrop').show();
$('select.sortddl').selectmenu('destroy');
$('select.sortddl').selectmenu({style:'dropdown'});
$('#resultsSection').append(innerShiv(response));
},
error: function (request, status, error) {
alert(request.statusText);
}});}});