I've been wondering the same thing for a while. The closest iteration of this I've come across so far is Session (https://getsession.org https://getsession.org)

I've been wondering the same thing for a while. The closest iteration of this I've come across so far is Session (https://getsession.org https://getsession.org) It routes messages through an Onion/TOR-like network of nodes that others volunteer to run. In return for running those nodes, they generate the Oxen cryptocurrency, similar to how mining Bitcoin works. This way, it's not fully centralized like WhatsApp/Telegram/etc, but also solves the issues of devices directly communicating, like what happens when the app isn't running on the phone.