function dIOS() {
return ( navigator.userAgent.match(/(iPhone|iPod|iPad)/i) );
}
$('.fancybox').fancybox({
******** your settings ********
afterShow: function() {
if ( dIOS() ) { $('body').css({'position': 'fixed'}); }
},
afterClose: function() {
if ( dIOS() ) { $('body').css({'position': ''}); }
}
});