Federation support?

I am not aware of such a feature. I could say that it is not supported.

Its a pity, I think there would be some interest

AFAIK it's not currently supported but the work on this feature is already underway and, if I'm not mistaken, the testing of it should start in this coming quarter. I'm a newbie (joined this Monday) so take this with a grain of salt. There's plenty of material on wiki already. Have a look at this page, for example: https://wiki.ringcentral.com/pages/viewpage.action?pageId=217917564