Persistent chat is only available for Cisco Jabber for Windows.
More details: http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/jabber/10_6/CJAB_BK_C56DE1AB_00_cisco-jabber-106-deployment-and-installation-guide/CJAB_BK_C56DE1AB_00_cisco-jabber-106-deployment-and_chapter_010010.html#JABW_TK_CBD6C8DE_00