How do I ONLY receive and send iMessage (not SMS)? Is this possible? I have an international phone plan that charges way too much money for international texts. I'd like to still be able to use iMessage instead of other texting apps, (but realize it will only be able to be with folks who have an iPhone and iMessage activated.) 

I believe I've figured out my settings so I only send iMessage, but I can not figure out how to FORCE receiving texts only through iMessage and not SMS.
Is this possible?
Might this have changed recently?

It appears now one can select to "send as SMS" when iMessage is unavailable (Settings > Messages on iPhone).  Perhaps now there is also a way to only have texts sent as iMessages only when being sent internationally, yet also have domestic (within country) texts sent as either iMessage and/or SMS?