To such folks from where the option will not be available, it is possible to activate it from the Google Lab functions located on that Gmail menu list. There are numerous simple steps you might want to adhere to for those who are to send SMS from Gmail. These include:
Key in your preferred contact name within the Search or invite friend’s field offered in chat. From the choices, opt for send SMS.
Enter the contact number in the dialog area that will can be seen under Send SMS message to the member field.
Click on save.
A chat window will show up the place where you can simply put any test message. Hit the Enter key also, the text is going to be sent out to a chosen cell phone number.