Voltaire, I have been using Skype (the free, computer to computer version) to chat with business partners all over the place. On broadband and when everyone's computer is working, it's fantastic. Also good for conference calls.
I use it with a microphone and loudspeakers but sometimes this can give you audio feedback problems unless you are carefull with microphone placement. I suspect a headset is the best way to go.
Skype also works well chatting to other computers internationally, beijing, thailand....
