Here is another one:
"WP Mobile Detect"
http://wordpress.org/extend/plugins/wp-mobile-detect
Impressing list of shortcodes:
http://wordpress.org/extend/plugins/wp-mobile-detect/faq/
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Well, I came to this thread because I need a similar solution:
I want to do a selection of the content depending on the theme (e.g. theme 1 for desktop, theme 2 for mobile).
like
[content_theme1][/content_theme1]
[content_theme2][/content_theme1]
Maybe it would be possible to add a function to one of the mentioned plugins which detects the theme and than filters the content!?