Related link: http://www.symbianone.com/content/view/2660/108/

Not yet officially available, however, Opera software have removed the download restrictions “temporarily” enabling users to download and test this nifty new web browser.
FYI:

Opera Mini is free to download and use and does not require any registration fee.
Your phone must be able to run Java applications, and GPRS Internet connections.
The Opera Mini server uses the same engine as desktop installs of Opera, so it has the same capabilities as Opera for desktop.
Opera Mini is expected to be officially launched in early 2006