However, we need to differentiate multiple aspects here:
- does the messenger allow users to use an XMPP client? This was possible on Facebook messenger for a while but was discontinued.
- does the messenger allow users to talk to XMPP users on other servers? This used to be possible with GTalk, but only if you didn't install Hangouts and only if the other server allowed unencrypted communication (which they typically don't since at least 2013). It's possible with Cisco and was possible with Lync/Skype for Business, but only after convincing your domain admin to whitelist the remote server.
- is it using XMPP under the hood? WhatsApp used to, before they mutilated the protocol. https://xmpp.org/uses/gaming.html lists some online gaming platforms that are technically XMPP, but it doesn't really matter for the users.
Quicksy answers to all these questions with a clear "yes", giving its users (and their friends!) more choices than any other phone number based IM system.
The post I replied to said:
> shows that xmpp really isn't behind centralized silo messengers in functionality and usability.
The siloed systems using non-federated XMPP (possibly with some private extensions) shows that it's technically very capable.