Nokia S40 devices have been coming preloaded with Opera Mini for a long while, but this might be coming to an end. Nokia Beta Labs have introduced the Ovi Browser for S40, which takes the same approach to browsing as Opera Mini does.
The browser is still in beta (as if "Nokia Beta Labs" didn't tip you off). Ovi Browser uses custom servers to open a page, compresses it and send the compressed version to your phone. Just like Opera Mini does.
If fact, at this point Ovi Browser looks very, very similar to Opera Mini 4.2 though Beta Labs didn't say if they've used Opera code and servers. The Ovi Browser beta lacks some features, but developers are working on adding new ones for the next beta so, we don't know what exactly will be included and what will be left out of the final version.
Check out this video to see the Ovi Browser in action:
So far, Ovi Browser features fast page loads transferring up to 90% less data, URL and form auto-filling, integration with search engines (Yahoo!, Google, Bing), bookmarks and others. Some of the features missing in action that we'd like to see added are tabs (though Opera Mini 4.2 doesn't have tabs either), find on page and saving pages.
If you want to test it out, open browser.ovi.com on your phone. To check the list of supported phones, open that page in your desktop browser or check on this page. There don't seem to be plans to bring Ovi Browser to Symbian. We guess you'll just have to keep using Opera Mobile if you're on S60 (not a huge loss).