Windows Phone is dead (even if its market share is >1%, I believe the project has been abandoned) and BlackBerry OS is hanging on but holds a trivial share of the market.
Duopoly? No, more like Apple and Google are the only good companies out there.
And that didn't came from anti-competitive behaviors, but from HARD WORK.
Things like Google Maps and Apple Stores are cold hard work that are really meaningful for people's quality of life.
Amazon and others don't give any of this to the consumer, that's the reason nobody wants to go with their platforms.