Distributed corporate collaboration tools

I'm looking for a corporate collaboration tool to help bring together my team, who are geographically and organisationally distributed. Some team members operate on client sites, behind corporate firewalls and similar.

The restrictions I have are:

• Must allow creation of persistent 'channels' (i.e. not just one-to-one or one-to-many chats).
• Must be free (or very close to it).
• Must be commonly available through corporate firewalls (i.e. operate on port 80 or similar). I'm aware no solution will be guaranteed to work through every firewall, but one that allows us to avoid the common restrictions is important.
• Must have a desktop/alert agent, to allow users to be alerted if/when new messages arrive in channels they are listening to.
• If at all possible, should have a feature to allow the app to start at login/boot time, so developers don't have to remember to activate it, or manually sign in.

Does anyone have any recommendations which meet these criteria?

I have so far considered:

• Google Talk: Fails the 'channels' test - group chats are also only available via the web interface.
• CampFire: Fails the desktop alert and auto-start function. Requires users to open web browser, navigate, log in, etc. Also fails the 'free' test, but only just. Price wouldn't be an object if these other failures could be overcome.
• www.24im.com: Fails the 'common corporate firewalls' test - this communicates on ports 10880-10889, which are blocked on all corporate firewalls we tested.

Just use Skype. It's free, it has excellent chatting capabilities, works over firewalls, supports lots of collaboration features out of box and plenty more as plugins.

P.S. It is also supported natively on Windows Mobile and has good clients on other mobile platforms (like Fring on S60)