I don't think it's right to count Windows Phone separately from Microsoft's previous mobile phone offerings. Even if it was a major change from before, it was still part of the lineage.
If you count it that way, Microsoft has been in the mobile phone OS business for well over a decade and they still have essentially no traction. They had traction back when the smartphone market was tiny, but they didn't expand with the market once Apple and Google blew it open.
If Google were still struggling to get traction with their search engine in 2010, I think it would be quite fair to say that Yahoo or whoever had won and maybe they should give it up.