In the aerogear.simplepush.js, where the notifier subscribe method happens, https://github.com/aerogear/aerogear-js/blob/master/src/simplepush/aerogear.simplepush.js#L94
the "callback" parameter, doesn't seem to be used at all. https://github.com/aerogear/aerogear-js/blob/master/src/notifier/adapters/simplePush.js#L372
probably can be removed