Here is how it works:
* * * This is how app will start * * *
~ No one can see app icon on app drawer. You have to dial a number from phone dial screen to open the app.
First time app can be opened from drawer after that app icon will be disappeared from your app drawer. So from next time you can open app by dialing a default number 1111 or you can set your own app start number from settings screen of app
~ To receive SMS in private sms app you have to add contact number from Contacts screen of app. So once you add any contact from your contacts list to app, all messages of that contact will be imported in app and remove from system sms app.
~ All the messages will be received in the app. (No message of private number will be received in system sms app).
~ By default there will not be any notification for private sms received. But you can add one from settings screen of app and you can also change notification message as per your requirement.
~ You can restore all message from app to system sms app by long clicking on contact of contact list in app.
~ NOTE: Removing app without restoring sms to system sms app will delete all sms and you'll lost your sms.
And there is no way to recover your app start number so please remember it carefully
~ you can send messages to any message conversation.