AFAIK you can only set the number for an SMS, not they body. So you
could send the user to the SMS editor, but he will have to fill in the
keyword himself (which is annoying). Unless you have your own
shortcode, but those can be expensive.
Also, most premium SMS services only work for one, or a few,
countries.
Good luck tho, and if you do manage to populate the body of the SMS,
let me know!
PanMan