You cannot install majority of applications.

You cannot install majority of applications.:
If you have a new phone or you have formatted your phone, you have to change the default setting first so that you can install applications that are not Symbian Signed. (To answer your following question, no, that does not mean you can install unsigned applications, only that you can install applications that do not require Signing).

On your phone, open the Menu and go to Tools/App.mgr.(application manager) and click on options/settings. Change the Software installation to 'All' and the Online certificate check to 'Off'.