Sending SMS from Gmail
You can send SMS messages to your contacts’ mobile phones using Gmail Chat. To do so from Gmail:
1. Enter your contact’s name in the ‘Search or invite friends’ box in Chat, and select Send SMS from the box of options that appears to the right of your contact’s name. Or, if you already have a Chat window open for this contact, just click Options, and select Send SMS.
2. In the dialog box, enter a phone number in the ‘Send SMS messages to this number’ field. For now, this feature works only on United States phone numbers. If you're outside the US, you can still use it, but you won't see the SMS option in Chat until you enable it manually in the Chat settings page.
3. Click Save.
4. A Chat window appears. Just type your message as you would normally. When you hit Enter, the message will be sent to the phone number you entered.
If your contact replies, the text message response will appear as a reply in Chat. These conversations are stored in your Chat history just like regular chats (but keep in mind that you can’t go off the record while communicating via SMS).
Note: depending on which mobile plans your contacts have, they may be charged by their mobile providers for receiving text messages.