I'll just use push notifications from here on out.
I used to love them and they still might be good for a little personal projects (though your story says otherwise) but I would never pick them to use at scale. At one point they said they needed the /exact/ text of every message we were going to send ahead of time to approve before we sent it... Yeah that doesn't work when you send OTPs (yes, yes, I know, we have to have it as a fallback) or a user-specific/transaction-specific url. So pretty much they only thing you could send is generic marketing trash, cool...
Twilio is forcing Tollfree Number registation and their current timeline is 6 weeks to approve. Well a week or 2 ago they decided that they wanted more data than what was currently submitted. So everyone is currently being denied and having to resubmit their registrations.
10DLC / Local numbers is madness in and of itself too. Forcing businesses to pay quarterly fees so these poor ol' carriers can have more recurring rev.