[eru]

Isn't iMessage just another OTT? (So I'm not sure what significance Apple vs non-Apple has here?)

Honestly, SMS today just exists as a legacy, because of status quo. Just like 'normal' phone calls.

Of course, both are still quite important in the real world.

[dools]

SMS is the only inter operable messaging standard. If you send a message from iMessage to someone with Android it goes via SMS.

[eru]

Well, it's inter-operable between mobile phones. But not between arbitrary devices in general. E-Mail is probably the closest to that ideal?

> If you send a message from iMessage to someone with Android it goes via SMS.

Interesting. I think there are some Android messaging apps that also fall back to SMS, but it's not a behaviour I would find particularly useful.