IcyMoustache,
can I suggest you try an XMPP gateway? Look at the list on:

http://www.jabberes.org/servers/

I use hot-chilli.net but there are plenty others. Sign in to one account (one net connection = less battery drain) and you get ICQ, Yahoo, AOL, Google talk, MSN & a few others... heck I think some of them support facebook chat even though it's not listed on that website (I don't use facebook). Not skype though.

You have to sign in to your XMPP account on a desktop machine to add each additional protocol ("transport") because the N900 interface doesn't let you do that. I used a program called gajim. Takes 5 mins, do that once & you're set.

My N900 is now a beast of a messenger!