To be honest, I think the above clients and services like Snikket fit that description.
Now, I wouldn’t say they’re all on the same level UX-wise as WhatsApp, Telegram etc. But I do think they are 90%-95% of the way there, and in my experience that’s enough to convince friends and family to switch over.
In my experience, when people haven’t wanted to switch, it’s normally not been because of the clients, but because they don’t want to install yet another app to talk to someone.
Monal comes close.