UPDATE (15th Sept. 2011) – A new very simple and fully working Symbian hacking method is now available for all S60 versions (including Symbian^3). So please refer to this post for the tutorial (no key/certificate, flashing or custom firmware required).
Note that following method will work only if you have your phone specific certificate and key ISSUED BEFORE 23rd June 2011. While the above method does not require any cer/key file.
Older hacking methods (like HelloOx) that worked well in older