Things you should know about Nokia 5800's Application

Symbian Applications .sis or .sisx (Signed)
Install using Application Installer found in OVI or PC Suite.

Symbian Applications .sis or .sisx (Unsigned) Get files Signed at Symbiansignedonline
Sign then install using Application Installer found in OVI or PC Suite.

Widget .wgz Files.
Install by moving to Phone or SD card Memory and select Open.

Java based Applications .jar & .jad Files
Install by moving to Phone or SD card Memory and Open from .jad or .jar (if .jad is not present)

Flash .swf Files
Install by moving to Phone or SD card Memory and Open

Certificate Problems
If you get error “Certificate Error, contact the application supplier”. To accept all applications Go to Settings > Application mgr. > Installation sett. Change Software installation from Signed Only to All and Online certificate check to Off.
If you get "Certificate Expired" Go to Settings > Phone > Date and Time and set the date to an earlier time, one year should be enough. You can change the date back after you have installed the application.