motorolas dont have themes like we are used to know them.
They just use the word themes because theyve learned watching s//e that its a good selling word

A motorolla theme is a wallpaper, a screensaver and a ringtone.
There are no themeeditor for the user - but you can buy some "themes" from motorolas homepage. Theres a total of 7 themes you can choose from last time I checked.
You could also create your own "theme" directly on the phone simply by choosing which wallpaper, screensaver and ringtone to use.
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Samsung dont offer any theming for their normal phones afaik
but like xpert mentioned microsoft powered smartphones does support themes.