[kupfer]

I'm surprised to hear xmpp on mobile works for people. I tried a few times with a friend. I'm on Android, she has an iPhone. And it always was too unreliable. The worst part is that half of the time messages are not delivered or very late. But there are also problems with attachments. We tried different clients and servers.

[southerntofu]

Yes it works, there's a bunch of standards (XEPs) describing how a client/server should handle unreliable connections, push notifications, etc. However, not all servers respect these. If you're setting up your own, it's easy to enable though.

Also a problem is iOS clients. Developing on iOS requires lock-in into the Apple ecosystem and most XMPP folks are free-software people so nobody will bother to buy Apple hardware/software specifically to develop for their closed ecosystem (i.e. unpaid labor for a multi-billion corporation), although i'm sure a lot of folks would be happy to do just that if that was sponsored work (donations, grants).

On Android, Conversations (or its forks Quicksy/Snikket) is the best. ChatSecure on iOS has been buggy for years (every time i tried with someone with an iPhone), but nowadays Siskin appears to be a good iOS client, though i haven't had the hardware/system to try it myself.