Jami has "Swarm" conversations, which are git-backed behind the scenes, and can be synchronized across multiple devices and/or participants seamlessly. Actually, thanks to the way Jami uses git, a subset of participants in a group conversation could enter a local network and continue chatting amongst themselves, and once they connect with the rest of the participants again their histories will automatically be synchronized and merged.

You can read more about Swarm here: https://jami.net/synchronizing-conversation-history-with-swa...

To add a new device, from account settings select 'Link another device'. This will create an encrypted archive of your account details and temporarily (for 10 minutes) put it on the OpenDHT network, and give you a PIN which you would use on your new device to have Jami retrieve and import your account. You could also do this manually and without going through OpenDHT, by having Jami create a local backup of your account on your current device, and then transfer the backup archive onto your new device yourself, and import it into Jami. After adding the new device, your Swarm conversations and their histories will begin synchronizing shortly.