Opera claimed to have an iPhone app ready back in 2008, held up only by Apple's pain-in-the-ass approval process. Curious, then, that they're just now showing it off at Mobile World Congress, alongside early builds of Opera Mobile for Android.
Alternative browsers on the iPhone aren't really alternative browsers, since historically they've all used the same version of the WebKit rendering engine as Mobile Safari. For Opera to release a version of Mini for the iPhone would be a big deal: assuming its using Opera's rendering engine and server-side compression tools, it could legitimately change the iPhone browsing experience for the first time since, well, launch.
Two things spark concern here: Opera's press materials don't mention Opera's Presto rendering engine by name (though that's not too shocking); and the software evidently will "not [be] publicly available" when its demoed in Barcelona next week. Honestly though, that could mean anything from a later release date to anxiety about the approval process, so there's no use reading too much into it right now. Today, Opera and iPhone are finally one. Nobody take that away from me. [Opera]