That may be the point, but it’s not working out that way. The spec is older than iMessage. It failed. Google just took it and made their own implementation. I’m not sure if Google’s RCS works with Verizon’s for example, I’m sure basic things do. AFAIK third party developers can’t implement it in their apps, so you have to have an Android phone to use it. Someone correct me if I’m wrong. The entire thing relies on Google to keep it running.