Set up Text Messaging (SMS) in Google Chat
Sign into your Gmail account. Click the green labs icon at the top right corner between your gmail ID and Settings. Alternatively, you can reach it by going to Settings and then click the Labs tab. The "Text Messaging (SMS) in Chat" feature appears near the bottom of the Labs page. Select "Enable" and "Save Changes."
That's it. The hard part comes in putting it to work especially as you connect with each user's phone for the first time.
In the Chat box in the sidebar, enter the name of the person you want to text. Either the person will show up in the list or in the case of a new contact, a pop up appears with Mail, Invite to chat, and Send SMS options. For those already in your contact list, you'll see a similar pop up with a couple of more options.
Select Send SMS and enter the mobile phone number, if it's not already filled for you. Click Save. A new chat window appears after saving -- maybe. This is one of the glitches for first-time Gmail SMS users (me included). The chat window may not show up -- it took a few tries before it finally did for me. Try restarting your browser. The feature may need a little time to wake up and take effect.
When you see the chat box, enter your message and hit Enter. Leave it at that until you receive a response. This way you have a second chance, if the first one doesn't take. Google's SMS feature won't let anyone send more than two messages to the same recipient until the recipient has replied. This can be a problem because the person may miss the messages. When this happens, you won't be able to send any other messages to the recipient. This happened to me and there was no way around it. I tried having my recipient text the phone number that appears on my recipients' screens when I send SMS from Gmail. It didn't work.