I understand that it may be problematic sometimes but this was very smooth. I didn’t even say anything.
A: what’s your number for the whatsapp group Me: I don’t have whatsapp because of facebook. B: ok, we have to use signal then A: ok
And that was it. Life can be very easy sometimes
If that’s the main problem then that’s easy to solve! Simply use a free public xmpp server.
I mention the self- and paid-hosting options because businesses tend to like having a sevice agreement backed by a contract, and may have additional specialised requirements not provided by free services (xmpp or otherwise).