In February 2006, Google launched Gmail Chat, a simple feature that lets you send instant messages inside of your browser. In February 2007, Yahoo integrates its messenger into Yahoo Mail Beta.
Yahoo Mail opens an IM conversation in a new tab inside Yahoo Mail, unlike Gmail that shows a small box at the bottom of the window (you can maximize it). You can also start to compose a mail and then convert it to an instant message or the opposite.
Yahoo hopes to attract more people to Yahoo Messenger, that only has 73 million users, compared to more than 250 million users for Yahoo Mail. Note that the new feature is available only for the Yahoo Mail Beta and will be slowly released to everyone in the weeks to come.
If anyone asks you what's Yahoo Mail Beta, here's the official definition: "The Yahoo! Mail beta is a true Web 2.0 experience, including a sleek, easy-to-use interface with the speed and responsiveness of a desktop application. In addition to instant messaging, the Yahoo! Mail beta also features enhanced functionality such as drag and drop e-mail organization, message preview, an integrated calendar and an RSS reader."