Shoutbox

I am thinking about writing a plugin that will analyze incoming packets, and, based on what they contain, perform different actions, such as:

When a user opens a chat window on their end, a toast will pop up informing you of this.
When the user you are chatting with closes their window, a toast pops up, or a message is displayed, informing you of this.

Other uses may come to light as I write this plugin.

My question is this: does the API provide this kind of functionality?

Thanks everyone!