I just found this on the @joinjabber’s website. It is using UnifiedPush to achieve this. All you have to do is go into settings in Conversations and enable UP for any XMPP account. It will use a service running at up.conversations.im by default, but you can use any service, including a self-hosted one if you have, instead.
Another great use for XMPP, I guess, besides having a great messaging service.
I just set up unified push with self hosting ntfy. The most.unfortunate part of unified push is the lack of apps that support it though.