import flash.events.Event;

var _lastFrame:String = this.currentLabel;

function enterFrameHandler(event:Event):void {
    if(this.currentLabel != _lastFrame) {
        _lastFrame = this.currentLabel; // set this equal to this.currentFrame to listen for any frame changes instead.
        dispatchEvent(new Event(Event.CHANGE));
    }
}
function changeHandler(event:Event):void {
    trace('the frame label changed to:' + this.currentLabel);
}

this.addEventListener(Event.ENTER_FRAME, enterFrameHandler);
this.addEventListener(Event.CHANGE, changeHandler);