Okay, it's just for facebook users!
You can put a Pingbox on your Facebook profile, and visitors to your page can IM you without having to download or sign into Yahoo Messenger.
To add a Pingbox to your page, visit the [Yahoo! Messenger Pingbox application page] or here on Facebook.The same customization tools are available in the Facebook version, so you can personalize your online and offline greeting, choose from dozens of designs, and if you wish, require your visitors to give themselves a nickname before they can IM you.
With the Pingbox app, your friends can IM you from your profile page even when you’re not on Facebook.