In my circles text is generally for when you want to get the message to someone right away, and email is for when they should read at their convenience.
I wish messaging apps gave the sender the ability to hint at urgency, like the priority header that some email clients support, and then the recipient would be able to use that (or choose to ignore it) instead of the relatively rudimentary controls typically available today.
A recipient can put their whole phone silent mode, vibrate mode, or ringtone mode; use DND mode, perhaps with a schedule, perhaps with exceptions for contacts; specify a ringtone per contact; mute specific group messages -- all of these have one thing in common, which is that if the sender has something unusually important or unusually unimportant to say, they're stuck with generating whatever type of notification the recipient already decided is appropriate for a typical message from that sender.
Using phone calls for higher urgency and email for lower urgency is usually good enough, but achieving that same effect in-band through a messaging app for continuity of history would be even better.
Except that's not how other people would perceive it. I've since learned that it can be incredibly annoying to others, to the point where some people would actually get distressed thinking they would have to answer the texts. Couple that with a bad habit of sending many short texts (it's how you'd write on messaging in the old days) and you have one REALLY REALLY ANNOYING FRIEND (regrettably I was that annoying friend).
So I guess I just want to apologize profusely from the other side of the fence. I'm trying to be much more mindful these days about whether that chit-chat message REALLY needs to be sent RIGHT NOW, or can it just wait for a conversation at a later time?
I'm trying to be much more self-aware in this regard.