I needed to find a workaround for that SMS problem this summer while my brother was in France (we have Sprint and his eKit SIM couldn't SMS to CDMA). I found
www.peekamo.com. That site is kind of strange at first, but you register an account for each phone, and then instead of texting directly, you send a SMS to Peekamo's access number for your country formatted as follows: "peek (username) (message)". Peekamo them forwards your message onto the specified person and they can reply the same way. It's basically an SMS proxy. The reason I really liked this service, apart from the fact that it made sending SMS from an international SIM to a CDMA carrier possible, is that this makes any outgoing text messages from the US phone free (as long as there's a texting plan on that line) since Peekamo's access number for the US is local. You can also send SMS messages if you log into your account on their site. It worked great this summer! Anyway, I think there's some other sites like Peekamo, but it's just the only one I've tried. Good luck!