Now you can keep the conversations going with a new Labs feature that lets you send SMS text messages right from Gmail. It combines the best parts of IM and texting: you chat from the comfort of your computer, and your friends can peck out replies on their little keyboards. Google is just trying it out for cell phones in the United States right now, but you can send texts to your friends with US phone numbers from anywhere in the world. You can find complete info at http://gmailblog.blogspot.com/2008/12/really-new-in-labs-this-time-sms-text.html
You can also add a task list, "superstars", and many other gadgets. Even a custom gadget can be made (Add any gadget by URL).
The service is available only in US. I think will be difficult for Google to enable user send sms through gmail on world level.
Haha,good for those who live in US but not for me who live outside.Hopefully google can expand the usage maybe for google adsense publisher only