This brand new Gmail Labs feature Labs lets you send Text SMS right from Gmail Inbox. It combines the best parts of IM and texting: you chat from the comfort of your computer, and your friends can peck out the replies on their little mobile keyboards.
How to Send SMS from Gmail
To send an SMS, You can simply type a US-phone number or into the search box in the chat window on the left, then select “Send SMS.” You can also select the contact you want to SMS first and then add their phone number.
Once you give us a name for that phone number, you’ll be able to start chatting.