Using the Twilio API to Send SMS
I setup an account with Twilio and was able to get a trial phone number and send a SMS message using curl in all of about 15 minutes. Their online console worked flawlessly and was very impressive.
I created a support ticket to ask specifically about RCS, even though it still seems to closed to general users.
I can probably develop my application using SMS, then upgrade to RCS whenever it is available. Not ideal though.