Feedback from APNS
The Apple Push Notification Service (APNS) tracks notifications that fail because the app is no longer installed on the device. Windows Azure Mobile Services enables you access this information from the APNS feedback service and remove device tokens so that you can avoid the extra cost of sending notifications to uninstalled apps. To do this, Mobile Services periodically calls the processFeedback function. In this function, you can call the getFeedback method on the apns object. This method returns array of objects that represent failures, where each object has deviceToken and timeStamp fields.