Use any messaging app and choose to make it default. Make core messaging functionality interoperable. They lay out concrete examples like file transfer.
I've read some things like this. Is it correct that messaging services will need to interoperate? WhatsApp, Messenger, iMessage? Would love to be able to message people that I can't easily reach now from Signal for instance.
Really goes for almost everything. I don't want my machines and appliances to be 'smart' and 'connected'. I just want them to do the thing I use them for, that's it.