Perhaps too little too late since everyone now uses messaging apps for practically no cost.
The pay-per-message model has simply no place here.
There are countries were SMS is actually local to the carrier, and they don't route user messages out of their bounds. In the olden days it was fun asking people where they contract their phone to decide wether to mail them or message them.
Some countries have horrible reliability for SMSes, I think India is a famous one. Trying to do user auth over SMS becomes a nightmare.
Then the issues if you cross borders, where you'll be enjoying both countries SMS idiosyncrasies on top of the round trip costs.
Then carriers won't open SMS to non voice SIMs, even if they get an access to the network. But you'll need to meet specific criteria to get a voice enabled SIM.
All in all, it's a tried and true protocol in limited setups, but not something to hold as a global gold standard (I think there sadly is no global standard to hold on a pedestal...we can hope we make one in the future)
Local monopolies rather than a global one.
What if there was a global, international messaging system available to everyone with a phone, that strove for five-nines reliability? And wasn't funded by advertising? And didn't deplatform anyone(+)?
Oh wait it's called SMS and everyone hates it, largely for good reasons. The internet has a lot of problems but it disrupted the telcos by being far cheaper despite using the same infrastructure while offering more capability.