If I may, I'd like to inject a plea for sanity here. Please, please, pretty please with sugar on top, don't reinvent the wheel when it comes to chat protocols. Right now, on my desktop, I have 5 different windows open dedicated to various chat networks and chat protocols. I have steam chat, a window with my irssi session, a pidgin session with connections to a slack session and an aim session, a telegram session, and a skype session. Yes, implementing someone else's protocols is complicated and sometimes painful, but when you end up needing a half dozen different /types/ of connections, there is something wrong and broken with how we're approaching the whole talk to other people thing.
There are business reasons why we have so many different protocols and apps. Everyone wants a piece of the pie and letting "your" users talk on someone else's network is seen as a risk. Your competitor might not want you on their network, either.
In the case of Apple, I'm pretty sure they aggressively ban anything that doesn't look like a real iDevice. I've heard the same of WhatsApp but I've successfully tested a couple of third party protocol implementations.
XMPP isn't great for mobile (bandwidth/battery usage) but I don't know enough to comment on that.
Have a browse back through some HN threads on chat and IM - these kinds of points come up every time. We've lost the war. One of my friends just asked me to install LINE and I'd be up to 6 different apps if I didn't just give up and go back to SMS.
The claim that XMPP on mobile can only result in lots of bandwith and battery usage is false, according to Daniel Gultsch, developer of the Android XMPP client conversations: https://gultsch.de/xmpp_2016.html
Money quote: “XMPP is not suited for mobile devices. That’s a myth that has been around for ages. It is mostly spread by people who want to sell you their own proprietary instant messaging solution.”
From my own experience, high battery usage is the fault of the XMPP client. Regarding bandwith, I have been chatting over throttled 3G and regular 2G connections. The initial connection takes noticeably longer, otherwise everything except file transfers seems fine.
You do not need to convince them to use a single client. The one must-have feature for mobile XMPP that many clients have built-in is message receipts (XEP-0184).
I have successfully used this for voice calls between the chat clients Gajim/Pidgin (I do not remember which) and Google Talk (the now-discontinued XMPP client by Google). I have also done video calls between two Nokia N900 phones, to see if it works. Voice and video via XMPP has worked since approximately 2009 and is just neglected by the companies for business reasons.
XMPP has the draft extension of Jingle, and there are Jingle extensions for things like file transfer. Similarly SIP/SIMPLE could be used, or WebRTC. Any of the three could be used instead of the mess we have now.
I am not aware of a good obvious default answer. And even when there is a reasonable one (ie xmpp for text chat) it doesn't appear that the open flavor has won in the market place.
Ever tried bitlbee? Not sure how well it's keeping up with the new protocols but years ago it was a way to consolidate at least a few of the older ones into a single application. Also not sure why this idea has not been replicated. Maybe it has.
The idea has been replicated in XMPP as so-called transports, which maps other protocols to XMPP. This arguably works better than bitlbee and other IRC gateways, since XMPP is a superset of many protocols, while IRC is a subset of many protocols.
https://en.wikipedia.org/wiki/XMPP#Connecting_to_other_proto...
I can join chatrooms in my XMPP client by joining a multi-user chat, like maemo%irc.freenode.net@irc.netlab.cz. It may seem useless at first, but I have found out that when on a train and using IRC directly, I timeout much more often than if using XMPP in the same situation.
In the "last generation" of chat apps, there were certainly a lot of multiprotocol messengers. Trillium and Pidgin come to mind, and were way more popular with bitlbee.
