sip/xmpp groupware clients interchangeable?

[1clue]

Hi,

There are a few threads on this but none of them really fit my situation, and I don't want to poach on somebody else's thread.

We have people on Macs, Windows and Linux. We all universally hate Skype, but it's the best non-paid solution.

We need:

1. Group or individual text chat, with topics.
   
2. Group or individual voice calling
   
3. Group or individual desktop sharing, like Skype or Webex.
   
4. File sharing (send files to a chat thread)
   
5. It would be really neat if we could get a whiteboard app too.
   

I was really excited about Jitsi but it turns out the Mac software is not acceptable. One thread got me interested about tox, but it's alpha stage, I need stuff that works. Looking through the rest, I don't see anything that has all the features I need. Desktop sharing is definitely a must-have, we do code reviews and such every day.

Again, Mac, windows and Linux. I'm at a loss, so I guess I have these questions about existing groupware:

1. Can clients be interchanged, meaning use one thing on Linux and another on Mac, as long as the same feature is supported?
   
2. How much of a pain is it to juggle one app with a whiteboard and another one with desktop sharing, and another with text chat?
   

Thanks.