Here is How to send Free SMS to any Mobile in any country using Gmail
First you need Gmail account for sending SMS. If not get create one and Sign in to it. Then open up the Chat pop up menu from the bottom left if it already isn't there. Click on the little arrow, and Add a new contact.
If you already have the contact which you want to send SMS, just skip this step
Now, right click on top of your contact and pres Send SMS button as depicts below.
But if you haven't sent that contact an SMS before, or if you haven't added their number, then instead of the Send SMS button, there will be a Chat button at the exact same position. Click on this button and you will see a small pop-up at the bottom right of your screen, as depicts below.
After Clicking Continue this chat over SMS button, Next screen will only be appeared if you haven't added their number, or haven't sent them an SMS before. Otherwise, you will be able to enter your SMS directly in to next pop up screen. Once you click the continue button, you will be prompted to choose a country and mobile. This is the contact's mobile number. Add a number and then save.
Once you have entered the mobile number, a pop-up will again appear at the bottom right exactly where the previous one did. This is your chat box. You are now ready to go! Type a message in the text field , hit Enter, and sit back and wait for your friend's reply!
This is a smart way Google has found to encourage the use of this service. Initially, you are given fifty credits, which means you can send out 50 messages. For every one message sent, one credit is deducted. But for every message received, say when someone replies to your Gmail text, you get 5 credits. So tell your friends to stop being miserly, and start replying to texts :). You can not, however, exceed the 50 credit limit, no matter how many replies you get.
What if you lose all the credits? Well, you will receive one credit after 24 hours. A smart way to increase your credits would be to send a text to your own mobile phone, and then replying to it any number of times to refill your credits!