It is trivial to implement. They don't do it because they make a ton of money every year selling origin spoofing to businesses and charging customers for incom

It is trivial to implement. They don't do it because they make a ton of money every year selling origin spoofing to businesses and charging customers for incoming texts (they never asked for). Spoofing is a service that the telcoms offer. Not a weakness! At least, that's how they see it.