jQuery Callback - Execute Function after loading Modal

Question

I have a hybrid mobile app using jQuery Mobile. At one point, in iOS, it loads a Modal window which contains a drop down box. I have a JavaScript function, in another file, that populates the drop down with different options, depending on a parameter. This works fine in Black Berry because it uses another page, instead of a modal, but in iOS the function to fill the drop down doesn't execute, I'm guessing its running before the the modal.

So I was reading about it and I think I need to use a Callback.

The modal gets initiated with:

app.modal.init(app.views.MODAL_REJECT);

I had tried to just call the function after it

getDropDownOptions(app.myvar);

But that didn't work.

How would I use a Callback in this case? I read about it but I really don't understand how to apply it.

Thanks

More Info / Update:

Something like this?:

    fromBT: function () {
        if (hwc.isIOS()) {

            var _callback = function () {
                mySelect = $('#reason-code');
                myOptions = {
                    1: 'AAAA',
                    2: 'BBBB',
                    3: 'CCCC',
                };
                $.each(myOptions, function (val, text) {
                    mySelect.append(
                        $('<option></option>').val(val).html(text)
                    );
                });
            }

            app.modal.init(app.views.MODAL_WINDOW(_callback));

        } else if(hwc.isBlackBerry()){
            app.loadPage(app.views.BB_PAGE, true);
        }  
    }

So fromBT is called by a button, if is iOS I open a Modal window, but I want to add options to a select/dropdown inside the modal window.