Okay, I don't really know why it didn't work before, but I blame the new safari ios debug console (which is now required to go trough safari on your mac), because it didn't always show all logs I sent to the console.
However, when I just appended the messages to the body of the html-document itself, the events WERE working. Binding the jQuery 'resize' event to the window seems to be the best option.
The document height is something around 200 when not full screen and when full screen it's 320.
The simplest solution seems to just work. (Just combine it with an orientation change function, to detect if the iPhone is in landscape mode (http://ajaxian.com/archives/iphone-windowonorientationchange-code)).
$(window).on('resize', function(){
if ($(this).height() > 300 &&
(window.orientation == 90 || window.orientation == -90)) {
// Full screen!
} else {
// Exit full screen!
}
});