Are you running a research-intensive startup? Are you afraid that your ideas might be “just in case” backed up whether you like it or not? Let me guess – you are also using one of the IM clients that’s on the “backup list”?
There is a solution to your problem – and that’s of course Open Source. If you wish to keep all your IM conversations in house, far away from 3rd party hands – just use Jabber (XMPP). There are clients supporting virtually every platform – and it can be integrated with asterisk giving you additional presence options in case you plan to run also in-house telephony.
A list of XMPP servers: http://en.wikipedia.org/wiki/Comparison_of_XMPP_server_software
Extensive list of IM clients: http://en.wikipedia.org/wiki/Comparison_of_instant_messaging_clients
What should you go for? If you need a super scalable solution for large deployments – and are not afraid of Erlang – go with ejabberd. If you are more on the C++ side and wish to use MySQL or PostgreSQL as backend out of the box – jabberd2 is your answer.
Both ejabberd and jabberd2 are available in Ubuntu. In CentOS only ejabberd is available in standard repo – for jabberd2 you have to resort to EPEL from Fedora Project (installation is a zero-trouble, tested at sysCore on CentOS 6.4).