Price and "good enough" performance will make inroads
I balked at buying my 13-year-old son an iPhone, so for $49, I got him a Nokia a couple years ago that proved capable enough for his needs and far more durable than the multiple iTouches he dropped and cracked. Well, that Nokia finally bit the dust when he dropped it while running, so we upgraded him to a Nokia 635 (must be old, as Microsoft is dropping the Nokia name). My son is more than happy with it, and he and a friend were recently marveling over the speaker quality while listening to a song I didn't exactly like hearing. "Sounds better than my iPhone 5C," admitted my son's friend.
I predict low cost and high value will eventually win Microsoft plenty of market share.