More than anything I would like to use open protocol for chatting. Personal communication is a mess. I currently have Hangouts, Facebook Messenger, Skype, Viber and Whatsapp on my phone. General folks use whatever is popular and XMPP is not really a choice. Moreover I looked into Jabber and the account sign-up page's certificate has expired and account sign-up has been inactive for close to a year. It is hard to establish trust over such a network.
Hangouts chat uses Jabber, Facebook Messenger uses XMPP. Skype uses a proprietary protocol, and licensing restrictions prohibit any unofficial client from connecting to the Microsoft severs. I don't know much about Viber or Whatsapp internals, but I would hazard that Viber is similar to Skype.
Chances are that you can connect with most people over Google or Facebook, but it's not perfect. If you are still using their servers, then it might defeat the purpose of avoiding their clients. You can use Off The Record (OTR) to avoid the privacy implications of using the servers with both of them, but none of the official clients support it, so they would have to use an alternative client as well, which defeats the purpose of using existing networks.
Hangouts doesn't actually really totally use Jabber. It supports it if a Jabber client is involved, but between Hangouts sessions they use some proprietary bullshit. That is why my chat history on, say, telepathy won't show up if I was using the Android hangouts app to message someone.
Also, there is literally no good foss voip and conferencing options. Jitsi videobridge is the closest thing I've found, and that isn't an XMPP standard and isn't supported by my preferred IM tools. Also, Jitsi is an ugly as sin Java app....
I'm definitely going to try putting aside a week this summer to see how hard it would be to implement videobridge in telepathy. If we could get that and group OTR encryption in it, there would finally be a FOSS communication alternative...
Jabber and XMPP are the same thing. WhatsApp uses a version of XMPP with just enough encryption to stop anyone from creating their own WhatsApp compatible client.
