When Android came to town... Blackberry = Strong in enterprise, generally weak everywhere else. Apple = Strong contender, but had serious issues with Job's 'deathgrip' (artificial limitations). Targets the top niche of the price range. Symbian = Weak brand name. Lots of hidden (buried?) capabilities. It was 'sold with the phone', imho they're much less so (not really?) a contender in this respect.
I don't see any reason why MeeGo should be a great smartphone OS, at least not for some time when HW has evolved some more.