Right now Google has decided to only treat the US crowd with the ability to send sms messages from inside of GMail,  But I think that is just do to the logistics and trying to control the amount of load that the service will be generating.  Google will not want to pull the service for a second time since people will most likely become frustrated with the service and adoption will be impeded.

Just like all features that Google enables.  They first must be enabled by going into the settings of your of your Gmail account.  This is the same process that we explained inside of our post on "How to Use Google Tasks In Gmail"

Ok so the first thing that you have to do is enable the "Text Messaging in Chat" option inside of your Gmail account.  Login to your Gmail account and then in the upper right hand corner click on the link that says "Settings".  Now this will open up the settings tab for your account. Now click on the tab that says "Labs" which is right next to "Themes" and "Web Clips" in your Gmail account.  Inside of the Labs section you are going to see a number of features that Google is releasing but I guess they don't feel is ready for primetime. Here is where you can enable the "Text Messaging in Chat Feature"

Now this feature will be enabled on the left hand side inside of the window that you normally use when chatting.  Pretty simple.  Now you can send chat messages to your friends phones and they will be automatically converted to SMS messages.  When they respond they show up inside your chat window.  Same as any othe Google chat user.

Now your friends arent going to see your name inside of the message.  Instead they are going to see a "406" area code number.  This is a unique ID .  So they can add it to there phone and text back to you whenever they want.  Its is a great setup.