In a recent project I had a form within an Iframe that needed to talk to the parent frame via postMessage. The parent frame was an angular application and I had to show and hide some content. I was able to access the scope outside angular and update via the angular.element() method (This is using version 1.4.2).
var scope = angular.element($("#someDOMElement")).scope();
scope.YourCTRL.showMessage = true;