Quote - Thanks.

By leaving the n-gons (under each button), I think the resulting subdivision defects might have accidentally added to the realism.

Wow.  That came out really cool. You could probably add a support loop to that ngon, and sharpen the buttons even more.  However, by leaving the ngon, there's a few creases that aren't visible.  It all depends on the kind of creasing you want.  Definitely experiment with different variations, for all kinds of cool results.  I like to add the buttons manually as seperate objects, but the way you did it also conserves polygon load.  Nice work!

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