> As an iPhone mobile / windows desktop user I would love an interoperable protocol so I could respond to texts from my desktop
You have MANY of them. SMS/MMS and Matrix spring to mind immediately. Mastodon qualifies. You can use RCS today if your carrier has an app like Verizon's Message+. If you want to go all retro, IRC.
That's ignoring the productized implementations all over the place - Signal, WhatsApp, Telegram, Messenger, Slack, Discord, and so on. MSN and ICQ are still running.
You have MANY of them. SMS/MMS and Matrix spring to mind immediately. Mastodon qualifies. You can use RCS today if your carrier has an app like Verizon's Message+. If you want to go all retro, IRC.
That's ignoring the productized implementations all over the place - Signal, WhatsApp, Telegram, Messenger, Slack, Discord, and so on. MSN and ICQ are still running.