I do this quite a bit for remote generators, hydro.
I looked at doing it directly and decided against it as I can't guarantee that I will always use a mobile data connection.
I always have Internet but it could be BB, Mobile, or Satellite. I pay for an email - SMS gateway, at about 2.5p / text.
This allows me to use the same code to send mail as I need for text, it is simply a matter of address.
Perhaps not what you want but probably worth considering when evaluating solutions.