Signal is the world’s most widely used truly private messaging app, and our cryptographic technologies provide extra layers of privacy beyond the Signal app itself. Since launching in 2013, the Signal Protocol—our end-to-end encryption technology—has become the de facto standard for private commu...
Except it is not free. My carrier does not include them in the main plans (because they’re not as commonplace anymore), and you either buy an additional package or pay per each SMS.
It’s free for them