Just guesses.
It makes me wonder when you route a landline number to a cellphone number if text messages might get routed as well.
also check with the landline provider if they offer text over landline service.

That also seems like something that suddenly stopped being a thing at all a couple of years back. Used to be the providers would have automated voice reading of SMS, but it evaporated from the standard services and nowhere does it seem to appear as an option to add. Doesn't help that all services here seem to be customer hostile these days and it's easier to cancel and start a new service with someone else than change a plan, and that's still a 2 month ordeal.