We have a slew of partners who have done this in the past...it just depends on what platform you are using and how you want it to work. There isn't a large selection of off-the-shelf solutions, so chances are high you may need to roll your own.
Guido Hofmann can speak to what is possible based on what they've done with Lotus Notes / Sametime.
Note: Depending on your solution, it may be possible to drop in an overlay using a Cartridges (Jive Anywhere) - Developer Resources cartridge, but again..all depends on what IM client you intend to use.
yes, there are some options. But as Ryan Rutan mentioned before: it really depends on the use case and it's requirements. However, i would be happy if we can provide some of our insights offline.
Thank you - Guido