Putting an App in Stealth Mode

This is my case scenario:

once my app is installed in a mobile device i need it to be stealth: no track of the app shall be visible on the phone, until the phone owner calls a certain 4 digits number at which point the app main window or/and app icon becomes visible and operative: would this be possible to achieve with b4a and could anybody plz point me into the right direction (library or/and code) in order to code such a feature?

Thanks in advance.