We are writing this useful Symbian Mobiles Tutorial because many people ask for signing unsigned applications / games but missing their needed Certificate, Key files (.cer & .key) for installing free downloaded .sis / .sisx Applications and games with their mobile iMEi # . So this short tutorial via screen shots guide you how to get your Symbian .cer and .key files for installing apps & games with free online.
Update: New Method to Kill Certificate & Key Files Sign Error Forever
How to:
1) First register OPDA Certificate site and login to your account.
2) After signing in, Click on My Certificate Link as screen shot below (Click to see Zoom)
3) Now click Apply .cer button.
4) Now complete the required information for your mobile model and IMEI#. 
5) Finally submit your application and your required .cer, .key files will be ready for download in few hours.
Note: One certificate and password key file always unique for one IMIE #, download these certificate and key files and save them with you forever which will help you to sign any application any time.
Now you can sign your unsigned .sis or .sisx files from Signing Soft link with the help of Certificate, Key files or you may also use SIS Signer v1.x and Pot Sign Tool PC Applications for this purpose.
Update: New Method to Kill Certificate & Key Files Sign Error Forever
Hi im ericson and i have a 5230. This is the emei 56051036338872 pls create my cert and key thanks