SMS are virtually free for every carrier. The prices for the customers exist to partially offset the fixed costs of the infrastructure (which already exists).
I agree that I don't trust governments today to provide the necessary confidentiality guarantees but remember that both physical mail and the phone network are government backed - in the sense that they set the rules even if they are operated by private entities in some countries.
I hear this sentiment a lot from people in the USA. They deeply distrust their government and can't imagine it being different anyway else in the world.