Whenever you install an application in a Symbian phone, it makes an entry in Application Manager, so that you can remove it later if required. Though it is a useful feature but sometimes it causes more harm then good, for example today even a child know how to operate a phone and anyone may (intentionally or accidentally) remove your installed applications through Application Manager. To avoid this disaster (or just for fun), here is a simple trick by which you can remove the installed applications entry from Application Manager:
Install a file explorer like X-plore in your phone
Run X-plore and go to the directory where you have installed the application (The one which you want to remove from Application Manager). For example if you installed the application in Memory Card then the go to E:/System and if the App is installed in phone memory then open C:/System‘ (if you are unsure where the Application was installed then go to Application Manager and highlight that application, now from Options Menu select ‘View Details’, there you can see where it is installed).
Open the subfolder “Install” under System folder. In this folder find the desired application’s name file. Either delete this file or cut and paste it somewhere outside System folder (you can again place that file in the above directory if you wish to get back the entry in App. Manager later on). Exit X-plore and done.
Now there won’t be any entry of the application in Application Manager.
NOTE: I have tried the above method in symbian Series 60 2nd Edition phones only. However it can also be applied in 3rd edition phones with change in folder paths.