Matrix. With its bridges you can “wire-in” networks like WhatsApp, Slack, Signal, Telegram, Discord, iMessage, SMS, e-mail, … and have a single app that interacts with them all. You can have a single group chat with users from all those networks participating and no one would be any the wiser.
Why? Existing platforms, especially the plain cell network, are going to be far more compatible and reliable.
Because this is SelfHosted and hosting services yourself is cool?
Some people have very legitimate reasons to want a secure private communication platform, and others are just enthusiastic nerds who do it for fun.
Cellphone network calls / texts aint secure at all. If you want to communicate in a secure way you need to use another seevice/app.
Many stated matriy as selfhostable service and i totally agree. Signal/Threema are also good options If you dont want to selhost.
Matrix. With its bridges you can “wire-in” networks like WhatsApp, Slack, Signal, Telegram, Discord, iMessage, SMS, e-mail, … and have a single app that interacts with them all. You can have a single group chat with users from all those networks participating and no one would be any the wiser.