How to detect user uninstalled iOS App? I need pus

I know Apple won't let you know user uninstalled your app.

My Problem
I have an old legacy SMS system to send alert Short Message to end user. Most of these messages are serious. Bottleneck is the GSM module has limitation when send hundreds SMS users simultaneously. Delay is inevitable.

Thus, I build a new alert system to send push notification to my users, if they installed my app. After register their phone number, their SMS Alert will be switched into new alert system.

Problem is some old school users prefer SMS rather than push notification. They download the app, and register their phone number. Then, they found their phone doesn't have 3G data plan. They deleted the app without un-register their phone number.

My new system has no idea who deleted app without unregister phone number. All serious alert messages still keep sending into the nonexistent app one their phones.

My Question
Is there any smart idea or mechanism can detect user have deleted my app?

APNS has a feedback service where Apple reports any device token that is no longer active on the users device. You are required by Apple to check the tokens from the feedback service and stop sending pushes to those devices.

You can use this same information to automatically move the user back to SMS. Just tie the device token to the phone number in your database. If the token is active, send pushes to it. If it is reported by the feedback service to be in-active, remove it from your records and use the users phone number for SMS again.

Just remember that a device token can become active again, at which point, it will be registered with you through the same mechanism it was the first time. Re-save it with the user and use push again.