open modal window from iframe into the parent

You can use JQuery plugin SimpleModal

There's an option called "appendTo", where you can tell where do you put your Modal. The only problem with that approach is that the modal's overlay appear with iframe's size, so you must give it your desired width and height after you open it.

$('#div-modal').modal({
    appendTo: $(window.parent.document).find('body'),
    overlayCss: {backgroundColor:"#333"}, // Optional overlay style
    overlayClose:true, 
});
// Set overlay's width
$(window.parent.document).find('#simplemodal-overlay').css('width', '100%');

If the div you want to open as a modal is in your parent window, you could replace $('#div-modal') with $(window.parent.document).find('#div-modal')