Yes - Gmail Chat now supports free SMS - but only for U.S. phones as of now.
I read about it here:
What's new in Gmail?
Excerpt from above page:
[ Text Messaging in Chat
Send SMS text messages right from Gmail. You chat from your comfy computer and reach your friends on the go; they get your messages as texts and can peck out replies on their little keyboards. ]
Here's the official Gmail blog post about it:
Really new in Labs this time: SMS Text Messaging for chat
Though the target is only U.S. phones for now, anyone anywhere can send SMS via this feature to someone with a U.S. phone, according to the post.
They also have ways to let you block such messages from a specific user or all users, from coming to your phone, if you wish. This could be useful for those mobile phone users who are on plans that charge them for incoming messages.
This new SMS-from-Gmail-chat feature could be pretty useful - hope they extend it to the whole world soon :)
TechCrunch also has a post about it here.