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...
Wait. Signal was an SMS client. It wouldn’t cost them anything for a user to send an SMS message. IIRC, they nixed the SMS feature for security reasons, not cost.
That’s what they told me when gave then feedback through their website.
There’s no free lunch and corporations aren’t the most trustworthy source of information though so maybe it was about cost.