do all of these devices have different resolutions or aspect ratios? you might want to look at your project properties.
the default is "letterbox scale" which is usually good, but when dealing with different resolutions it can create some black spaces appear.
what you're showing makes me think its not set to letterbox.. maybe something else. I like (for landscape) scale inner.. although this does cause some information on the left and right to get cut off, it always fills the vertical space so you have no black space. just takes your game to be a centered design that accounts for missing space.
This is a bit extreme and shows a lot of different aspect ratios, but it does demonstrate how the black boxes can appear when you use different screen sizes and different aspect ratios http://www.rtings.com/images/black-bars ... mawide.png