kevintwohy:

Once the option is turned on, start typing a phone number into Chat’s search box and you’ll see the option to send an SMS.

If you already have your friend’s phone number stored in your Google account’s contacts, try searching for them by name. When your friend’s name appears in the drop-down list of contacts, you’ll see an option to send them an SMS. You can also hover over or click on anyone in your Chat buddy list to send them an SMS.

The first time you send a text message, it will appear on the person’s phone as coming from a number in the 406 area code. Google has made several thousands of these numbers available for Gmail users, and once a number is associated with your account, all of the text messages you send through Gmail will come from that number.

The 406 number works both ways, so your friend can reply to you via text message. Also, your friend can save that number in their phone as belonging to you, and they can even use it to initiate new chats with you.

Nice. Maybe I’ll start using GMail more. (I do love my Thunderbird, but GChat and SMS are pretty enticing.)