As people have several devices, they end up using multiple clients for the same chat account. While there are several ways and/or xmpp hacks to provide synchronized message history on all devices, Carbons is one of the more supported extensions (which is at least also used by Xabber). Maybe it would be nice to extend Kopetes XMPP support to include the optional feature of enabling Carbons: http://xmpp.org/extensions/xep-0280.html This allows for a standardized way of sharing conversations between different xmpp resources/devices.
Patches for such feature are really welcome!
Dear user, unfortunately Kopete is no longer maintained. Please migrate to another solution, e.g. for Jabber a possibility is Kaidan, for Matrix a candidate is NeoChat.