You lost me at SMS.
(If anyone has any hacks to get on FirstNet, I’d love to hear them)
WhatsApp is ubiquitous, at least among millenials and above. I'm not sure what the zoomers are up to. It's unavoidable for parents especially because parent groups exist for everything from kindergarten to sports. Usage may decline in the years to come over Meta's data protection issues but there's no end in sight.
(Sorry if I missed that you had already tried or are planning those)