monopoly doesn't mean that you cannot go elsewhere, it has to do with the reality that when an entity has such a dominant position in the market they are not the same as if they wouldn't have been. Often this comes with extra constraints on how they are allowed to behave, such as using their dominance in one market to buy their way into others, or how they charge for services.
As far as units sold, iOS makes up about 14% of the market, Android makes up 85% and a majority of apps sold are via Googles App Store.
As far as units sold, iOS makes up about 14% of the market, Android makes up 85% and a majority of apps sold are via Googles App Store.