I've been seeing stuff about Skype, so I had to check it out- and I'm pretty impressed.
It's like instant messaging, but with telephone quality voice. Instead of getting pinged with a "Gotta second?" IM, your computer will ring. You just need a headset and some friends who have also downloaded Skype to get started.
The folks behind KaZaA are behind Skype and it uses peer-to-peer technology. This makes the calls free.
I love watching new technologies that come along and upend an established industry like Napster/KazaA, TiVo, diamond technology (as reported in Wired). I'm hoping to see Skype represent a similar disruptive technology for the long-distance industry.