Most businesses, consumers, and developers universally continue to ignore the primary reason that iMessage is a closed platform, rather than an app on every platform as iTunes is: Apple is using device serial numbers for anti-spam, supported by a fully-authenticated hardware and software stack that does not allow user modification. This permits Apple to simply “console ban” any Apple device that spams on iMessage. Th…
My iPhone gets plenty of spam SMS messages, alongside my iMessage chats. The sanctity of iMessage communications doesn't stop that.
Swapping SMS for RCS support messages doesn't increase the spam surface.