Yahoo Messenger is moving into the free, PC-to-PC calling realm with its upcoming Beta release for Vista. There will be paid calling options as well. The most interesting part of this integration, at least visually, will likely be the WPF 3D integration, taking full advantage of all the Vista-ness that's been made available. I'm not sure how much you'll be wanting to see the visual effects that play on your computer while you talk to someone, but I suppose it's better than nothing.
[img src="" caption="" credit="" alt=""]
[img src="" caption="" credit="" alt=""]A feature I'm a tad more excited about is SMS integration, which will allow you to send text messages from Yahoo Messenger on Vista to your friend's mobile phone. At least it will be free for you. The good thing about this option is that the end receiver doesn't have to rely on a mobile instant messaging option on their phone in order to chat. Some IM clients already work like text messaging, so this isn't an entirely novel concept here, but it's always good to bring about more uniformity in the various options that are out there. Also included in the next Beta release for Vista are Mail alerts.